Sarah and Jamie McCauley are landlords, YouTubers, Walmart pallet flippers, eBay resellers and Amazon product reviewers — and those are just their active streams of income.

The McCauleys make their money by researching what makes side hustles profitable, testing them and teaching others how to do the same on YouTube. The Grand Rapids, Michigan-based couple earned nearly $140,000 from eight streams of income last year, according to documents reviewed by CNBC Make It.

They’re particularly good at two types of gigs, they say: anything involving real estate and their YouTube channel itself, where they share their side hustle exploits with at least 146,000 subscribers.

“If you’re looking to just make some extra money on the side, maybe pay off a credit card debt or pay for a vacation, I think that is doable for nearly everybody,” says Jamie.

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The McCauleys are part of a side hustle revolution, a growing number of Americans who supplement income with multiple jobs. More U.S adults — about 39%, according to Bankrate — have side hustles today than ever before, whether out of necessity, precaution or a desire to increase their earning power.

Ease of starting is at an all-time high: Platforms like Amazon, Airbnb and Fiverr offer instant access to paying customers. But with competition also rising, it’s hard to build a side hustle that regularly brings in revenue.

Make It spoke with a selection of Americans with successful side hustles to learn how they built their businesses, and used them to fund a wide variety of financial goals. Every respondent highlighted four common traits that helped drive their success:

No matter what you sell, you need people willing to buy it. Jenny Woo says her side hustle is successful for a simple reason: She researches her audiences intensely, and tailors her products specifically to them.

Woo is an adjunct lecturer at the University of California, Irvine, a freelance business consultant and the teacher of an online course about emotional intelligence. Her one-woman side hustle, called Mind Brain Emotion, sells 12 different emotional intelligence-themed card games.

It brought in $1.71 million on Amazon last year, according to documents reviewed by Make It.

Woo’s first deck of cards, “52 Essential Conversations,” was tailored toward parents who — like her — wanted to connect with their kids and build their emotional intelligence skills. She joined parenting Facebook groups and observed users’ posting, commenting and liking habits, she says.

After selling $10,000 worth of the game in a 2018 Kickstarter campaign, Woo kept researching. She conducted a survey of her consumers, and learned that “overwhelmed” teachers looking to support children’s social and emotional development made up a significant portion of her audience, she says.

Her second deck, “52 Essential Relationship Skills,” was built for those teachers. It didn’t sell as well as her first deck, but it taught Woo that she could broaden, and combine, her audiences.

Woo applied that lesson to her third game, “52 Coping Skills.” She started with her own experiences working with college students during the Covid-19 pandemic and combined it with her continued research on teachers and parents, she says.

It’s now Mind Brain Emotion’s top-selling game, says Woo.

Woo sells on Amazon, which has a broad reach, to collectively rope in Mind Brain Emotion’s hyper-specific audiences. Tim Riegel’s products have a more singular customer base, so he sells on Etsy, a marketplace known largely for homemade and handmade goods.

Riegel, a full-time general manager at a sheltered workshop, makes firepits from recycled tank ends in Lamar, Missouri, and sells them under the name Mozark Fire Pits. His average product weighs 225 pounds, and sells for $950.

Mozark Fire Pits brought in approximately $202,000 on Etsy last year, according to documents reviewed by Make It. Riegel maintains a 40% profit margin, he says.

Riegel chose Etsy over platforms like Amazon, Wayfair and Overstock because it felt more user-friendly, and a better fit for his personalized products, he says. He also sells on Facebook Marketplace, which costs him more in advertising — but less in shipping costs for customers within a 200-mile radius, he adds.

That kind of platform analysis is valuable, no matter what kind of side hustle you run.

If you sell a service, instead of a good, you might consider platforms like Fiverr and Upwork — popular among photo editors, marketing writers and voiceover artists — or Taskrabbit, known for labor-intensive side hustles like cleaning or repair work.

Or, opt out of those platforms entirely. If your gig is something that many other people also do, try finding marketplaces with more narrow niches like Contently, Skyword or ServiceScape, recommends side hustle expert Kathy Kristof.

“One of the problems I see with a lot of freelancers is that they go to the best-known online platforms … and those platforms are so saturated with people who have been there for, often, decades,” says Kristof, whose blog SideHusl has reviewed more than 500 different side gigs.

No matter your platform, you’ll need to stand out. A good listing can help: clear and concise, written for your intended audience, free of typos, with high-quality graphics and some search engine optimization (SEO).

Becky Powell, a kindergarten teacher based in Beaverton, Oregon, has a side hustle selling worksheets for other educators on an online platform called Teachers Pay Teachers. Many of her worksheets focus on her personal specialty, teaching children sight-reading skills.

Her side hustle didn’t take off until she embraced SEO. When she uploaded her first worksheets, she titled them, “Creating sight words with pattern blocks.” Sales slowly trickled in.

Her husband Jerome, who has a business background, suggested a simpler title, like “Hands-on sight words.” The sight-reading worksheets quickly became her bestselling products, Powell says.

Powell’s store brought in $125,500 in 2022 revenue, according to documents reviewed by Make It. Her husband also sells worksheets on the platform, and they’ve used their combined earnings to fund vacations and pay down their mortgage and student loans, Powell says.

“You have to have passion and knowledge,” she says. “You also have to have a business sense [and understand] SEO.”

Once you gain enough customers, work to turn your sales into positive reviews, so you appear higher in platforms’ search results, Kristof advises. Customer service, prompt shipping and quality control can usually earn you a good online reputation.

The McCauleys have a rule for their ever-changing collection of side hustles: “You either have to be one of the first to get there, or your approach has to be very unique and different to be successful,” Sarah says.

But being first or unique doesn’t guarantee long-term success. In 2020, the couple was early to a side hustle trend: pallet flipping. At local warehouses, they’d buy pallets of returned goods from Amazon, Walmart or Target. They’d unbox the pallets, discover their contents and resell the items for a hopeful profit.

From December 2020 to December 2022, the McCauleys made about $19,500 in pallet-flipping profits, they estimate. Their most popular unboxing YouTube video got 5.4 million viewers, translating to an additional $30,000 in advertising revenue, says Jamie.

Last year, more Americans hopped on the pallet-flipping trend. Pallet prices rose, resale values dropped and a slew of unboxing videos diluted the McCauleys’ viewership. “The pallets became not really worth our time … from the standpoint of time over money,” says Sarah.

Four years ago, the McCauleys would’ve simply moved onto their next side hustle. Now, they’re feeling the strain of constantly building new gigs from scratch, and starting to reorganize their income streams into a smaller number of longer-term projects.

Instead of flipping their current home renovation project in Northern Michigan for a profit, for example — something they’ve done multiple times — they’ll keep it as their own vacation house and part-time Airbnb rental, they say.

“We always knew [side hustling] was going to have an expiration date,” says Jamie. “It’s a young person’s game, to always be looking for what’s next.”

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Almost 60% of the caloric intake of the average American diet is coming from ultra-processed foods, according to a 2017 paper published in the journal Population Health Metrics — and that’s concerning to health experts.

“Ultra-processed foods contain ingredients that we generally wouldn’t find in our kitchen, and they often contain high amounts of sugar and salt,” says Jinan Banna, registered dietitian and professor of nutrition at the University of Hawaii.

“They may also contain additives, and they often are stripped of their nutritional values. So they may have very little vitamins and minerals [and] fiber.”

Eating ultra-processed foods often can lead to a higher risk of developing health conditions like dementia, type 2 diabetes and heart disease, according to doctors in the American Medical Association.

That’s why Banna limits her consumption of ultra-processed foods and encourages you to do the same. Here’s the highly processed food that she never consumes.

“Some [ultra-processed foods] I would never consume, such as soda,” Banna tells CNBC Make It.

“Soda doesn’t have any nutritional value other than just calories in the form of sugar. So they’re empty calories, which don’t give us any of the nutrients that we need.”

When you drink soda, it is digested very quickly and can cause you to feel hungry, she adds, which can lead you to eat more food than you planned to.

Instead of soda, Banna opts for different types of tea and water, still or sparkling.

“Sometimes I drink a cold hibiscus tea. Plain water, of course, is a great alternative,” she says. “Even coffee can be an option, of course, consumed in moderation.”

A recent preliminary study that was presented last week at a meeting held annually for the American Society for Nutrition took a close look at dietary data collected in 1995 from more than 500,000 Americans between the ages of 50 and 71. The data was used to determine if there were connections between dietary choices and mortality rates over the span of almost 30 years.

Out of 124 foods, ultra-processed drinks was the No. 1 food that people who had the highest intake of ultra-processed foods consumed.

“Diet soft drinks were the key contributor to ultra-processed food consumption. The second one was sugary soft drinks,” the study’s lead author Erikka Loftfield told CNN.

Beverages make up a significant portion of dietary intake. So, these types of drinks — like diet sodas and energy drinks — are the processed food that people seem to consume more than others, Loftfield said.

The study also found that the lifespans of those who eat a diet high in ultra-processed foods may be shortened by over 10%, according to CNN.

As a rule of thumb, Banna recommends using the 5/20 method when checking the nutrition labels on the foods you eat.

“You can use the daily value,” she says. “That’s an easy way to know whether the food is generally high or low in a particular nutrient.”

Check the daily value percentages of specific nutrients like sodium, sugars or saturated fat, Banna suggests.

“The idea is, if [it’s] 5% or less, then the food is generally low in that particular nutrient. If 20% or more, you can consider the food high [in the nutrient],” she says.

“So that’s just a quick way to glance at the label and know if a food contains a little bit or a lot.”

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As a single person, you’ll need an annual income of $40,000 to cover basic expenses in the cheapest U.S. states, according to a recent SmartAsset analysis.

The state with the lowest costs of living is West Virginia, closely followed by Arkansas and Oklahoma, the analysis says. In West Virginia, a one-person household needs a pre-tax income of $39,386 to pay for necessities like housing, transportation, health care, taxes and other common expenses — as tracked by the MIT Living Wage calculator.

The good news: The median American yearly wage for full-time workers is nearly $60,000, according to the Bureau of Labor Statistics. But minimum wage workers in many of the least-expensive U.S. states lag significantly behind that figure. With a 40-hour workweek, West Virginia’s $8.75 hourly minimum wage translates to just $18,200 per year, for example.

Here’s a look at the 15 U.S. states with the lowest cost of living, based on how much a single person needs to cover basic costs:

1. West Virginia: $39,386
2. Arkansas: $39,724
3. Oklahoma: $40,211
4. North Dakota: $40,262
5. Kentucky: $40,355
6. Ohio: $40,359
7. South Dakota: $40,718
8. Louisiana: $41,233
9. Mississippi: $41,361
10. Iowa: $41,678
11. New Mexico: $41,807
12. Nebraska: $41,849
13. Alabama: $41,911
14. Missouri: $42,024
15. Wisconsin: $42,062

Based on a 40-hour workweek, these totals work out to an hourly wage that ranges from about $19 to $20. In contrast, the most expensive state for a single person is Massachusetts, where a single person needs $58,009 per year to cover basic costs. That works out to roughly $28 per hour.

While rural states have lower costs, they tend to have lower wages, too. The median household income in West Virginia is $52,460, compared with $75,910 in New York, according to the Bureau of Labor Statistics’ most recent data from 2022.

The difference in basic costs between states is largely due to housing, which tends to be most affordable in rural states. Urban areas typically offer a higher concentration of jobs, attracting more residents — and increased housing demand drives up home prices.

Annual housing costs in heavily urban states like California and New York are close to $20,000, compared to roughly half that figure in the 15 least expensive states.

Rural states also tend to have lower taxes than states with large cities, because their public services and infrastructure are less expensive. Taxes vary by about $5,000 to $10,000 per year between states, according to SmartAsset’s analysis.

MIT’s Living Wage calculator is based on data from various federal agencies, adjusted for inflation as of December 2023.

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Expats in Denmark are among the happiest with their work lives, according to the latest Expat Insider survey from InterNations, the online global community for people who’ve moved abroad.

The Nordic country ranks No. 1 for where people are most satisfied with their jobs, career opportunities and work-life balance, among other aspects.

That’s based on survey responses from more than 12,500 people living in foreign countries and reflects their feelings on four broad categories covering work topics, including their career prospects, salary and job security, work culture and satisfaction, and work and leisure.

Denmark ranks highest for two groupings: work culture and satisfaction, as well as work and leisure.

Some 84% of expats in Denmark are satisfied with their work-life balance, compared to a global average of 60%; a similar share are happy with their work hours and, on average, work 39.2 hours per week, compared with 42.5 hours for the global average.

Here are the top 10 countries where expats are happiest with their work lives abroad:

1. Denmark
2. Saudi Arabia
3. Belgium
4. Netherlands
5. Luxembourg
6. United Arab Emirates
7. Australia
8. Mexico
9. Indonesia
10. Austria

Ilana Buhl, a CNBC Make It contributor and American teacher who moved to Denmark, says moving from Texas to Copenhagen brought about lots of positive changes to her work life: shorter workweeks, stronger boundaries around off-hours, five weeks of paid vacation, and a better salary to cover a lower cost of living.

Outside of work, she also enjoys robust public transit, public health care, affordable day care, and ample maternity leave paid for by her employer and the government.

Many of these factors contribute to the fact that Denmark consistently ranks as one of the happiest countries in the world, according to the annual World Happiness Report.

Coming in at No. 2 is Saudi Arabia, where a majority, 75%, say moving there has improved their career prospects, versus 56% globally. The majority, 63%, of newcomers relocate to Saudi Arabia for work, where they say they’re satisfied with the state of the local economy.

Meanwhile, just 35% of expats around the world say they moved to a foreign country for job-related reasons.

The biggest downside to working in Saudi Arabia may be the long hours — expats working there report logging 47.8 hours a week for a full-time job.

Rounding out the top three is Belgium, where expats are highly satisfied with their job security, the local job market and their own career opportunities.

Expats in Belgium say they enjoy flexibility in the workplace, especially among the 68% who say they can work remotely, and their shorter-than-average full-time workweek of 40.8 hours.

Panama was recognized as the No. 1 best country for expats overall, according to the InterNations survey. The overall ranking accounts for broader life and financial factors, where foreigners say they’re satisfied with the quality of life, ease of settling in, working abroad, personal finance and an “expat essentials” index, which covers housing, administration, language and digital life.

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When it comes to booking flights, travel experts are just like the rest of us.

Katy Nastro has visited more than 40 countries around the world. For the most part, she finds her flights through the Google Flights search engine.

As a frequent flyer and travel expert at Going, Nastro has a number of techniques she employs to find the best and most affordable flights she can.

Part of what makes Google Flights Nastro’s preferred flight booking destination is the ability it gives her to customize her search. When she is planning a trip, Nastro doesn’t stop at entering her destination and dates. She’ll toggle settings to sort by nonstop flights, preferred airlines and will potentially set a price threshold. 

“I put in all of my filters to make sure that I’m looking at as close to perfection as possible,” Nastro tells CNBC Make It. 

Here are three tips from Nastro to book flights like a pro.

Keeping your options open is one of the most important things you can do to help yourself find the best travel deals.

“I think flexibility is the biggest thing people need to remember,” Nastro says. “Google Flights has the functions within it to make it as easy as possible for you to explore all your options.”

For example, Nastro prefers to look at one-way flights rather than round-trip when she is first planning a journey. This is helpful not only for comparing prices, but also for figuring out if she can get as close to her desired flight times as possible. 

“If you’re really looking to prioritize traveling more affordably you should open your search up to the idea that you could fly out on your preferred airline but it might be cheaper to fly back on another,” she says. 

When she punches in a destination, Nastro doesn’t just stick to that city’s local airport. She adds different airports in the area as well, even if they might be a bus or train journey away from where she wants to go. 

“It really gives you the capability to widen your net,” she says. With more options, you can decide if flying out of your way is worth the savings. “Do I really want to prioritize my cost savings with the time that it’s going to take me to get to these alternate airports? Maybe. If the cost saving is significant enough.” 

When searching for international flights, Nastro is aware that Google may serve her options that have “super long layovers or multi-stop flights that nobody is really looking for.” To avoid getting her hopes up for a low price on a suboptimal flight, she plans ahead. 

“When I’m searching, I’m always making sure that I put in layover duration and toggle which connecting airports I will and won’t fly through,” she says. 

“Yes, you might be able to get a cheaper flight if you have a longer layover,” she adds. “But unless you’re going to be able to leave the airport and have enough time to do so, it might not be worth that time sitting in the airport.” 

Google Flights has a feature that shows you pricing history for a flight you’re looking at, as well as predictions of how the price will fluctuate in the future. But be careful about relying too much on this information, especially during a record-breaking travel season.

“It’s tough to say that Google Flights is 100% accurate all of the time,” Nastro says. “It’s giving you an estimation based off of history, which is pretty good, but it doesn’t mean that past history is going to deliver future results.”

Deciding when to pull the trigger and book your flights may depend on when you’re looking. If you’re in the Goldilocks window — the time frame during which you’re most likely to find the best prices to a given destination — you should feel comfortable booking with the knowledge that prices are only likely to go up from there.

“For peak seasons like the summer, we recommend booking between three and seven months out for domestic trips and between four and 10 months for international trips,” she says. 

But if you’re booking on short notice, don’t gamble on a sudden price drop.

“If you’re looking to book a flight in two weeks, it’s probably best to book it immediately if you’re comfortable with the price rather than wait another week,” she says. 

Once her flights are booked, Nastro still keeps price alerts on. 

“Because we have largely done away with change fees on legacy carriers in the US, if you booked a main economy ticket you can call and have that flight rebooked at that lower price and then get a credit,” she says. “I did this the other day and got a credit that I’m going to use towards a flight in August.”

Nastro configures her settings to give her alerts not only for the flight she already booked, but for all flights that day for the trip she wants to take.

“It’s likely not the case, but if it’s cheaper to fly on a different airline, I fly enough that it would make sense to pocket the travel credit to be used in the future and then book that cheaper ticket,” Nastro says.

And as much as she prefers Google Flights, Nastro will still check other sites as well.

“Sometimes Google Flights doesn’t display the absolute lowest fair that could be available on a really small [online travel agency],” she says. “You can use other search sites like Skyscanner or Momondo that could be $200 more in savings.”

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