There are a lot of ways to build wealth. You can squirrel your savings under the mattress, invest in real estate, or buy bonds and bank CDs to generate interest income, to name a few ideas. But of all the investment vehicles available, the stock market has been the most consistent wealth creator over the long run.

Since 1980, the benchmark S&P 500 has delivered an average annual total return (including dividends) of better than 11%. Keep in mind that this figure takes into account Black Monday, the dot-com crash, the Great Recession, and the coronavirus crash.

Perhaps the best thing about the stock market is you don't need to have the investing intellect of Warren Buffett to achieve financial independence. Simply buying game-changing businesses and holding onto them for long periods of time is the key that can allow the average investor to become a millionaire. It's my belief that the following four stocks can help John and Jane Q. Investor reach this financial milestone.

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Square

First up is fintech stock Square (NYSE:SQ), which is leading the War on Cash and the digital payments revolution. Even though Square has rocketed higher since the coronavirus pandemic, cashless payment growth is still in the very early stages.

For roughly a decade, Square's seller ecosystem has been its foundation. This is the operating segment that provides point-of-sale devices and analytics to help businesses succeed. Driven by merchant fees, the seller ecosystem has grown from $6.5 billion in gross payment volume (GPV) in 2012 to what'll likely be well over $130 billion in 2021, based on the $33.1 billion in GPV traversing its network in Q1 2021. 

What's more, we're seeing bigger businesses latch onto the seller ecosystem. In the first quarter, 61% of all GPV came from businesses with at least $125,000 in annualized GPV, compared to 52% in the comparable quarter two years earlier. Square isn't just for small merchants anymore.

However, it's digital peer-to-peer platform Cash App that should have your attention. Cash App's monthly active user count more than quintupled to 36 million by the end of 2020, with gross profit per user clocking in at $41, compared to less than $5 in costs to attract each new user. Cash App gives Square a number of new ways to generate revenue (e.g., Bitcoin trading), and it's quickly become the company's leading generator of gross profit.

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Teladoc Health

Innovative healthcare stocks are a good bet to make patient investors rich over the long run. With this in mind, there's a very good chance that telemedicine kingpin Teladoc Health (NYSE:TDOC) can help the average investor in their quest to reach millionaire status.

If you think Teladoc was in the right place at the right time during the pandemic, you wouldn't be wrong. Virtual visits on its platform catapulted from 4.14 million in 2019 to 10.59 million last year. But this is much more than just a pandemic play, as evidenced by the company's 74% average annual sales growth between 2013 and 2019.

Telehealth services offer a number of sustainable advantages that'll make it a mainstay in the U.S. treatment landscape. For one, virtual visits are considerably more convenient for patients than office visits. Conversely, it's also easier for doctors to keep tabs on their sickest/chronically ill patients via virtual consultations. While this convenience won't replace all medical visits, it does take a step forward in improving patient outcomes, which insurance companies are bound to appreciate (i.e., less money out of their pockets).

The Teladoc growth story also includes the cash-and-stock acquisition of Livongo Health in the fourth quarter of 2020. Livongo is a leading applied health signals company with approximately 658,000 diabetes members, as of March 2021.  Livongo collects copious amount of data on patients and with the help of artificial intelligence sends them tips to help them lead healthier lives. Despite being in the early stages of its growth, Livongo was profitable on a recurring basis at the time of its acquisition.

A veterinarian holding a small dog in her arms.

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Trupanion

The average investor can also make a boatload of money betting on an industry where spending never seems to decline: pets. That's why companion animal health insurer Trupanion (NASDAQ:TRUP) can be a millionaire-maker.

According to the American Pet Products Association, almost $110 billion is estimated to be spent on companion animals in 2021, with over $32 billion going toward veterinary care and product sales. It's been no less than a quarter of a century since year-over-year pet expenditures declined in the United States, which makes the pet industry about as surefire a growth trend as exists in this country. With pet owners willing to do whatever is necessary to keep their four-legged family members as healthy as possible, Trupanion is a no-brainer buy

When the first quarter came to a close, Trupanion had approximately 944,000 enrolled pets, some 610,000 of which were on a monthly subscription service.  Both figures have been consistently growing by a double-digit percentage. But what's crazy to think about is Trupanion has only penetrated about 1% of the U.S. pet market. If it were to simply match the U.K., where 25% of pet owners buy insurance for their furry family member, Trupanion would have an addressable market of over $32 billion.

Trupanion has competitive advantages, too. It's been building rapport with veterinarians at the clinical level for two decades, and it offers software to clinics that can handle payment at the time of service. Trupanion may be the tiny tot on this list, in terms of market cap, but it packs incredible "paw-tential."

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Sea Limited

Finally, look to Singapore-based large-cap stock Sea Limited (NYSE:SE) to deliver for the patient average investor over the long run. Sea's success is a reflection of its three (yes, three) rapidly growing operating segments.

At the moment, Sea's digital entertainment division is the only one of the three generating positive earnings before interest, taxes, depreciation, and amortization (EBITDA). In particular, Sea's mobile games have been a global hit, with the company nearing 649 million quarterly active gaming users as of the end of March. What's far more important is that 12.3% of these users were paying to play, which is a significantly higher conversion rate of pay-to-play than the mobile gaming industry average. 

Arguably the most-exciting of the three segments is e-commerce platform Shopee. It's currently the most-downloaded shopping app in Southeastern Asia, and it's rapidly gaining steam in Brazil. With a focus on fast-growing emerging markets with burgeoning middle classes, Shopee has seen the amount of merchandise purchased on its platform skyrocket from $10 billion in all of 2018 to $12.6 billion in just the first quarter of 2021.

The third operating segment of interest is digital financial services. As of March, Sea had more than 26 million people paying for mobile wallet services. With many emerging market countries underbanked, mobile wallets provide a means to access basic banking services.

Look for Sea Limited to be one of the fastest-growing large-cap stocks on the planet this decade.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.