"Slow and steady wins the race" is an adage that applies to many areas of life, not least to investing. Better to plant the acorn and watch it grow into a mighty oak over the years than get involved in a get-rich-quick scheme that promises you fantastic wealth in a short amount of time only to leave you poorer at the end of the day. 

Vivint Solar (VSLR), Micron Technology (MU -1.72%), and American Outdoor Brands (SWBI -0.45%) are all examples of acorns you can plant in your portfolio today and watch as they mature into mighty investments that will double your money over time. Read on to find out why our Foolish contributors like these stocks.

Solar energy's best value play

Travis Hoium (Vivint Solar): A decade ago, it was still expensive to install solar on your roof, but costs have come down so far that customers can buy a solar system with $0 down and get either lease or loan financing from installers. Vivint Solar is one of the leading installers in the country, with 183.8 megawatts installed in the past year. 

For investors, Vivint Solar could be a big winner in solar for a number of reasons, but the two I want to focus on here are the value it has on its balance sheet and the strong position it has as energy storage grows.

Traditionally, most of Vivint Solar's installations are financed through a lease or power purchase agreement where the company pays for the solar system on a customer's home and the customer agrees to pay for the electricity it delivers over 20 years or more. When you add up all of the cash flows from that transaction and discount them to today's dollars, you get a measure of value called retained value. It's a flawed measure in some ways, as I point out here, but retained value can give us an idea of how much value a solar company has on the balance sheet.

What's great about Vivint Solar's stock today is that it trades at a steep discount to retained value. Management estimates that at the end of 2017, it had $6.67 in net retained value per share on the balance sheet, compared to shares trading for $4.10. That's a steal for a solar stock, and don't forget that retained value will continue to rise as the company installs solar systems.

What excites me about Vivint Solar is energy storage combined with rooftop solar. Vivint Solar has a unique scale in the solar industry that can help it finance energy storage systems and drive value from batteries in a home. Companies who can link thousands of energy storage systems together will be able to create a virtual power plant and sell services like peak power or backup generation to the grid. Vivint Solar is one of only a few companies with the scale to offer that kind of energy storage service, which should help it generate revenue from systems it installs. 

In the long term, the solar business is going to continue to grow and Vivint Solar's residential solar and energy storage offerings are leading the way. The fact that investors get the stock at a discount to retained value is just icing on the cake. 

If you want a double, you probably want to look at tech stocks

Rich Smith (Micron Technology): How do you find a stock with the potential to double your money? I'm probably stating the obvious here, but it helps to start by looking for stocks that cost less than half what they're worth. And the way I go about that is by seeking out stocks selling for a cheap valuation, one where their price-to-free-cash-flow ratio is less than half their projected rate of percentage growth.

One of the biggest names in computer memory, Micron Technology is anything but a small company, boasting a market capitalization of $58.5 billion. And yet, despite its size, Micron stock really isn't that expensive. Last year, the company earned GAAP profits of $10 billion, giving it a price-to-earnings ratio of just 5.85. Free cash flow wasn't quite so robust, but at $7 billion, FCF wasn't too shabby either.

Best of all, when you compare Micron's P/FCF ratio of just 8.4 to analysts' projected long-term rate of profits growth -- 20%-plus -- it turns out that Micron stock is selling for a P/FCF/growth ratio of just 0.4. At that valuation, Micro stock could double...and still be cheaper than the value investors' touchstone of a P/FCF/growth ratio of 1.

Granted, for this to happen, DRAM and NAND memory prices have to hold firm, and Micron and its rivals have to avoid getting themselves stuck in another profit-sucking price war. But with Micron stock selling so cheaply today, that's a bet I'd be willing to make.

On target for growth

Rich Duprey (American Outdoor Brands): Gun manufacturer American Outdoor Brands trades as if it's just about ready to go out of business, but this financially secure outfit should soon see shares rocket higher.

Since the U.S. presidential election in 2016, gun sales have been in a funk from the loss of panic buying, which tended to send sales higher. A nominally pro-gun president and Congress has minimized the threat of extensive new gun control legislation getting approved. But that might not last much longer, as approaching midterm elections could tilt the balance of power against guns. The fear of that happening could send sales soaring once more.

In fact, it's already happening. After the tragic Parkland school shooting in Florida and President Trump's nominal support for more gun restrictions, sales have turned higher. Criminal background checks performed by the FBI in March were the highest they've ever been for that month since the law enforcement agency began keeping track in the late 1990s. Even the adjusted numbers from the National Shooting Sports Foundation, which provide a more accurate assessment of demand and sales, showed a near 11% increase for March, which is on par with the figure seen for the month back in 2013, the largest number ever.

What this suggests is that gunmakers like American Outdoor and Sturm, Ruger will soon see increase demand from distributors who supply retailers, which have been keeping their inventories low due to the slack demand.

The industry might not return to its record-breaking levels of 2016, and for the long-term health of the industry that's good, but it also means these historically depressed valuations we're seeing on the owner of the Smith & Wesson brand won't be around much longer either. Trading at just 19 times earnings and 17 times next year's estimates, American Outdoor Brands stock also costs only a fraction of its sales -- and with those about ready to rise, the disparity will only deepen.