But how do you know what's worth saving? Though no one can say for sure which objects will be popular and valuable to future collectors, here are 12 good bets.
Best things to collect for investment
1. Funko Pop figures
If you've never heard of Funko Pops, just dive into the nearest group of kids or collectors and ask for an explainer. What you'll hear is that Pops are cool vinyl toys that depict celebrities, or characters from movies and TV.
While many Funko Pops are mass-produced, others are made in very small quantities and are usually available only at toy fairs, Comic-Con events and more.
Some of the rarer figures have netted staggering returns. A Chewbacca figure released at Comic-Con in San Diego in 2011 recently fetched $2,700 on eBay. Based on the usual retail price of about $20, that's a 13,400% profit!
2. McDonald's items
McDonald's Happy Meal toys have been known to set off collector frenzies, but more mundane items from Mickey D's can be worth putting aside, too, especially if they're scarce or are likely to disappear.
The fast-food giant has begun shifting from plastic straws to paper ones, because of environmental concerns. In the U.K., where paper straws are already a thing, someone on eBay recently paid the equivalent of nearly $100 for 400 of the plastic sippers.
Other examples of why you might want to save stuff from McDonald's: The old-school mini coffee spoons that were discontinued years ago and a limited-edition Szechuan dipping sauce for McNuggets also sell for surprisingly high prices.
3. Recent first edition books
Having the ability to spot a future best-seller right out the gate can be a talent worth a great deal of cash.
When a new book's first edition is printed, publishers tend to release just a relatively small number of copies in order to gauge public demand. Consequently, first editions of popular books such as the Harry Potter series are relatively rare and sell for hundreds of dollars.
So if you were one of the lucky few who took a chance on a first-edition copy of Twilight, The Da Vinci Code or George R.R. Martin's A Game of Thrones, consider it a good investment. (Though obviously no substitute for a real investment account.)
4. Cereal boxes
Are you sure you want to toss that empty cereal box in your recycling bin? You might want to put it in the back of the closet instead, to sell it later on.
The history of pop culture can be told through cereal boxes, and collectors pay big money for vintage specimens featuring celebrities, popular cartoon characters, or unusual mail-away or in-the-box prizes.
Boxes with images of the Beatles have sold for thousands of dollars over the years. Recently, an unopened cereal box from 1989 with a hologram of Nintendo characters on the front fetched close to $1,000.
5. A first-gen Alexa (Amazon Echo)
Anyone who still has a first-generation Amazon Echo speaker with Alexa and is thinking of upgrading should not toss out the old one or drop it off at the nearest thrift store. In fact, you might want to go buy an older model, if you can find one — and stash it away.
At the rate the technology is growing, it's likely that a first-gen Echo may quickly seem like a relic. And the good news? People dig relics.
Case in point: Someone on eBay recent shelled out $250 for an in-the-box Motorola StarTAC flip phone, like the one you had in the 1990s. Hello?
6. 2016 election newspapers
About the only thing that people across political lines agree on about the 2016 presidential election is that the outcome was stunning. It was one of those turning-point moments likely to go down in U.S. history.
Americans wanting to own a piece of that history are already buying up newspapers from Nov. 9, 2016, the morning after Election Day. Copies of The Wall Street Journal have been selling on eBay for up to $30.
Years from now, they could be worth more. Presidential election newspapers from the 1980s routinely go for up to $45, Poynter reports, and the legendary "Dewey Defeats Truman" error front page from 1948 can be worth thousands.
7. Instant photos
Though practically every phone now gives you the ability to take pictures, people are still buying cameras, including Polaroid-style instant cameras that will print you a photo on the spot.
Those instant pics are worth saving, judging from the current interest in old Polaroids and old 35 mm photo slides. It's true: In the future, someone may want to pay for your old vacation snapshots!
Look around on eBay and you'll see that some individual Polaroid photos sell for as much as $10 each, and slides of tourist attractions, vintage trains and beach scenes go for up to $50 apiece.
8. Designer goods from mass retailers
Every now and then, a mass-market retailer such as Target, H&M and Uniqlo will partner with a celebrity or a design house — and shelves and racks are quickly emptied.
In 2015, Target stores offered special items from the resortwear company Lilly Pulitzer, and the merch sold out almost instantly. It was a similar story in 2007, when H&M rolled out a line designed by Madonna.
Often, these collaborations are "limited editions," and supply and demand does its thing. So get up early, grab your best credit card, and stand in line for this stuff, because you can be rewarded with a nice profit that will only go up with time.
9. Dyson Supersonic hairdryer
Rest assured that you're not alone if you're thinking, Seriously? A hairdryer? Though it may seem odd, the recently released Dyson Supersonic hairdryer may be worth keeping for the long haul, because it might one day be considered iconic.
The sleek, revolutionary design is reminiscent of the eye-catching personal electronics products introduced by Panasonic in the 1960s and '70s — which now bring good prices.
For example, a red, circular Panasonic Toot-a-Loop radio in the box recently sold for $135, and a green one without the box went for $110.50.
10. Nintendo DS
You can still score a brand-new Nintendo DS for well under $100 online. And if there's anything we've learned from video gaming technology, it's that what's cheap today may be worth a nice chunk of change down the line.
As gaming systems are trashed in favor of newer models, the old ones become far rarer as the decades roll on. And there will always be people out there keen on reliving their childhoods — and paying for the privilege.
So, for example, some original Atari sets now sell for hundreds to thousands of dollars.
11. Today's sneakers
There's a huge market for first-edition or limited-release sneakers, which are traded like a form of currency. And, as with bottles of fine wine, brand-new or even gently used sneakers often go up in value over the years.
This tends to be especially true for limited-edition styles from Nike or Adidas. What's new today may become a valuable vintage item before long.
Used, original Nike Air Jordan 1's from 1985 can go for more than $1,500, and a mint-condition pair in the box recently sold on eBay for close to $4,000. The original retail price? About $65.
12. First gen iPod Shuffle
Much like the Amazon Echo, a first-generation iPod Shuffle has the potential to become a sought-after collectors' item.
At the moment, you can score a new first-gen Shuffle still sealed in the original box for under $100 on eBay. That won't do much damage to your bank account. But as time passes and fewer of them remain in existence, the price will go up.
That's happened with the first-generation Sony Walkman personal cassette tape player from 1979. One of those recently fetched nearly $800 — thanks in part to the gadget's appearances in the Guardians of the Galaxy movies.