Retailers love to sell gift cards: They get to collect money upfront for future purchases; they tie gift recipients into buying stuff from them rather than a competing retailer; and—perhaps most important—there’s a decent chance the card will get lost or forgotten, and the company will realize a near-100-percent profit from the transaction.

So, tip #1: Use the card! According to a recent survey by CreditCards.com, 47 percent of U.S. adults say they have at least one unused gift card, voucher, or store credit, adding up to $21 billion in unused gift cards sitting in wallets and dresser drawers nationwide.

And use it soon. The faster you act, the less likely you are to forget about or lose that asset.

If you can, register it with the retailer. Some retailers allow you to apply the gift card value to an existing store account. Do so and the next time you buy something the company will automatically remind you about the gift-card credit—and you don’t have to worry about toting around or losing your cards.

Watch out for the spending trap. Retailers also love gift cards because they entice many shoppers to spend more than the value of their cards. They know we’ll tend to buy enough stuff so that we “use up” the full amount of any gift amounts. Plan out your purchases so that your cost stays close to the gifted value.

Shop around. Just because someone gave you free money doesn’t mean you should neglect to get the best deal. Don’t fall for fake sales (most sale prices aren’t special at all, just efforts by stores to manipulate their customers to spend). Read our articles here at Checkbook.org for advice on getting the best price on specific types of products, plus check out our top tips for getting the best price when shopping online. Find a better price elsewhere? Ask your gift-card retailer to match it.

Save documentation. If you are given a receipt with your gift card, save it. It may be the only proof you have of the card’s value if for any reason the card doesn’t work.

Check expiration dates. There’s a good federal law that protects the value of your card. The Credit Card Accountability, Responsibility and Disclosure Act mandates that gift cards must retain their full value for five years from the date of purchase. But gift cards issued by credit card companies like Visa and MasterCard can have shorter expiration dates—and many do.

Regift or resell, rather than wasting it. If you don’t think you’ll use the gift card, consider regifting it or even selling it. Reseller sites such as CardCash.com and Raise.com buy up partially used and unwanted gift cards and resell them. These sites won’t pay out anywhere near the full value for your card, but anything is better than shoving it in your kitchen junk drawer and forgetting about it.

Become a Smarter Consumer Get free, expert advice delivered to your inbox every Wednesday when you sign up for the Weekly Checklist newsletter.