For Wall Street and retail investors, this has been a challenging year like none before it. Whether you're a novice investor or someone who's seen their fair share of recessions, there's simply nothing that could have prepared folks for the disruption caused by the coronavirus disease 2019 (COVID-19) pandemic.

In what can be best described as a tale of two halves, the first quarter featured the fastest bear market decline in stock market history. Comparatively, the second quarter yielded the most robust quarterly gains for the benchmark S&P 500 since 1998.

Though periods of panic and heightened volatility can be naturally unnerving, they're often great news for long-term investors. That's because it allows those with a long-term mindset to pick up great businesses at a discount.

A businessman in a suit holding a potted plant in the shape of a dollar sign.

Image source: Getty Images.

Of course, the best stocks to buy aren't always those with the biggest brand-name. Patient investors can often find the juiciest long-term gains by purchasing faster-growing, but higher-risk small-cap stocks. If you have $2,000 in disposable cash that won't be used to pay bills or cover emergencies, then you have more than enough capital to invest in the following three small-cap stocks, which, in my view, have what it takes to make investors rich.

Aimmune Therapeutics

The first potential small-cap moneymaker is specialized biotech company Aimmune Therapeutics (NASDAQ:AIMT).

Aimmune made history on Jan. 31, 2020, when it secured the very first U.S. Food and Drug Administration approval for the treatment of peanut allergy in children and teens. The drug, Palforzia, works by desensitizing patients to the allergy over time. Though it doesn't cure a peanut allergy, it can help prevent severe reactions. In late-stage trials, 67% of patients taking Palforzia completed the study, which suggests they were able to tolerate increasing doses of peanut protein. By comparison, a meager 4% of those in the placebo group completed the study. In other words, the efficacy of Aimmune's lead drug isn't in question.

However, Aimmune has lost more than half of its value in 2020. This is primarily the result of COVID-19 halting the launch of Palforzia. Since the initial dose needs to be given in a clinical setting, and most hospitals are off-limits due to COVID-19, it's hurt initial uptake of the drug. That and a $10,000 wholesale list price is nothing to scoff at.

But having a clear pathway to market share in an indication that possesses blockbuster potential is nothing to sneeze at. As many as 6% of children in the U.S. have some form of peanut allergy. With some analysts calling for more than $1 billion in peak annual sales, Palforzia could well be Aimmune's golden ticket to a much loftier valuation.

A gloved processor using scissors to trim a cannabis flower.

Image source: Getty Images.

Cresco Labs

I get it -- owning cannabis stocks hasn't been a fruitful venture over the past 15 months. Regulatory-based supply issues in Canada and high tax rates in the U.S. market have allowed illicit channels to continue thriving throughout North America. But this doesn't change the fact that, as the marijuana industry matures, winners are going to emerge. Right now, Cresco Labs (OTC:CRLB.F) has the makings of a long-term winner.

Cresco Labs is a U.S. multistate operator that controls the seed-to-sale process. It has 18 operational dispensaries, with eight of those located in Illinois. The Land of Lincoln is particularly attractive to Cresco given that it opened its doors to adult-use weed sales on Jan. 1, 2020. By 2024, Illinois should be generating in excess of $1 billion in pot sales per year. Market share is certainly up for grabs in this key market, and Cresco is aiming to grab the bull by the horns. 

However, the biggest growth driver for Cresco Labs might just be its all-share acquisition of Origin House. The deal, which closed in January, gave Cresco access to Origin House's cannabis distribution license in California. There are only a handful of businesses in the Golden State licensed to move marijuana from Point A to B, and Cresco is now one. What's particularly important about this is it allows Cresco to push its products into nearly 600 dispensaries in the most valuable marijuana market in the U.S. (and world).

As one final note, Cresco Labs has not been shy about leaning on sale-leaseback agreements to boost its available cash, and was one of the few lucky pot stocks to gain access to nondilutive forms of financing. Whereas money is a concern for some cannabis stocks, it shouldn't be for Cresco.

A store associate using a point-of-sale interface on a monitor.

Image source: Getty Images.

Shift4 Payments

Last, but certainly not least, investors with $2,000 in disposable cash should consider investing in recent initial public offering Shift4 Payments (NYSE:FOUR).

Shift4 is part of the exceptionally hot fintech industry that's focused on moving consumers and enterprises away from cash. Despite being an under-the-radar name in the point-of-sale space, it's responsible for processing more than $200 billion in payment volume every year, which is actually double what Square's seller ecosystem did in 2019 ($106.2 billion). Shift4's point-of-sale solutions are probably best-known in the hospitality industry, which includes restaurants and hotels. Considering that the U.S. is a consumption-driven economy, generating fee-based revenue from payment solutions is often a winning formula.

But make no mistake about it, Shift4 is about more than just payments. It's also a technology solutions company. Shift4's Skytab mobile payments solution offers consumers the ability to order or pay at their table in restaurants, and can be integrated with Lighthouse 5, Shift4's cloud-based business intelligence tool that provides enterprises with actionable spending and pricing analytics. In other words, Shift4's business model is built on a suite of products, and not just its payment platform.

At the moment, Shift4 isn't profitable, primarily because it's reinvesting aggressively in technology solutions. But it's worth noting that subscription-based revenue, and revenue tied to its more than 7,000 software partners, is growing as a percentage of total sales. Wall Street loves double-digit sales growth with recurring revenue, and that's what Shift4 investors are going to get.