For most investors, a few hundred bucks isn't a make-or-break amount of money. When you're talking about a few thousand bucks though, things change. It can take a while to save up that sort of cash stash. As such, it really shouldn't be squandered. That's particularly true when you're talking about building a retirement nest egg. You can't go back and buy more time, after all, so you have to do things right while you're in your working years.

With that as the backdrop, here's a closer look at a couple of well-suited picks for your serious retirement money you know you won't be needing to access anytime soon. They're both well-proven outfits in industries that have been around for a while, and industries that will certainly be around in the distant future. You can feel comfortable about parking $5,000 in each (or some divisor of that total in the two together) and tucking these stocks away for a few years -- or maybe even a couple of decades.

1. Nvidia

You know the company. Nvidia's (NVDA -0.01%) graphics cards helped usher in the personal computer era back in the 1990s. It's still the leader of the stand-alone graphics processing unit (GPU) market, in fact, although computer visualization is no longer its breadwinner.

As it turns out, the same qualities required for graphics cards to handle the details of video games, animations, and other visual processing make them perfectly suited to handling the processing power requirements of artificial intelligence (AI) software. While estimates vary, analysts agree that Nvidia's processors are found in at least 80% of the world's AI computers. Indeed, purchases for artificial intelligence uses now account for more than half of Nvidia's total revenue -- revenue that's expected to grow by 47% in its current fiscal year, and another 27% next year.

There's still much more growth on the table, though.

For all the hype that AI has generated to date, the world has only scratched the surface of this potential market. Precedence Research believes the entirety of the AI industry was worth $120 billion last year, but forecasts it will reach a value of nearly $1.6 trillion by 2030. Hardware is going to be a key component of that growth, too, since physical platforms are ultimately required to handle the mountains of data processing required by AI applications. That's why Precedence Research further forecasts that the AI hardware market alone will grow from a little over $10 billion in 2021 to nearly $90 billion by 2030.

Assuming nothing changes in terms of technical capabilities, Nvidia should reap the bulk of this market growth. Of course, it's not like artificial intelligence (in one form or another) is ever likely to simply cease being used. It's evolving into a perma-industry, similar to banking or healthcare. That's the kind of scenario that makes for great long-term holdings. 

Value-minded investors should be warned that Nvidia shares aren't cheap. The stock is priced at nearly 60 times this year's projected per-share earnings, and over 40 times next year's earnings estimate. That's rich, to be sure.

This is one of those cases, however, where a company's performance and prospects merit such a valuation. Nvidia shares have been priced at these sorts of frothy multiples since it reinvented itself back in 2018, and the stock has rallied in spite of its steep valuations most of the time since then. It's unlikely we'll see a sudden change of heart from the market about its lofty valuation anytime soon. So you might as well buy now.

2. Merck is more diversified than you think

Pharmaceutical giant Merck (MRK 0.30%) is at the extreme other end of the growth and valuation spectrum. But that doesn't make it any less ownership-worthy than Nvidia.

It's one of the world's oldest, biggest, and best-known drugmakers, and the $275 billion market cap company sold almost $60 billion worth of pharmaceuticals last year, led by cancer drug Keytruda's revenue of nearly $21 billion. And that's a worry for some would-be investors looking for a long-term pick from the pharmaceutical sector.

Although it's not a completely unique story, AbbVie has become something of a poster child for drug companies that don't continually replenish their pipelines. At one point its hugely successful arthritis and colitis treatment Humira accounted for roughly half of its top line. With Humira's patent protection now all but effectively gone though, AbbVie's hyper-reliance on the drug's revenue has turned into a major liability. That's why the past few years have been very stressful and uncertain for AbbVie's shareholders ... and it could have been even worse.

What many investors may not fully see, however, is that Merck is already preparing for the time when Keytruda isn't the powerhouse revenue generator that it is today, even though that time is many, many years down the road.

Case in point: Although it's been obscured by other news, Merck's late-stage pipeline of cardiovascular drug candidates has tripled in size over the course of the past year. The company's looking for its current cardiovascular R&D efforts to drive more than $10 billion in new annual sales by the 2030s. In the meantime, 2021's $11.5 billion acquisition of Acceleron Pharma is also poised to finally pay off. The pulmonary arterial hypertension drug Sotatercept that Merck picked up as part of that deal is showing strong results in phase 3 trials. Merck also recently inked a deal with Opko Health to co-develop an Epstein-Barr vaccine. Right now, there are no vaccines for that virus, but if there were, Coherent Market Insights suggests the market could be worth on the order of $2 billion per year.

These developments should ease the minds of retirement-minded investors worried that Merck isn't looking far enough into the future. The thing is, Merck is perpetually replenishing its pipeline and putting new drugs on the market. It's structured to do so, in fact.

Better still, the forward-thinking company not only generates enough cash flow to fully fund this growth, but it pays a nice dividend as well. The current quarterly payout of $0.73 per share translates into a yield of 2.6% at recent share prices, and management has raised the payout for 12 consecutive years. These are the kinds of characteristics you want from a stock you plan to hold for decades.