Gift cards make great stocking stuffers — just as long as you don’t stuff them in a drawer and forget about them after the holidays. Americans are expected to spend nearly $30 billion on gift cards this holiday season, according to the National Retail Federation. Restaurant gift cards are the most popular, making up one-third of those sales.

Most of those gift cards will be redeemed. Paytronix, which tracks restaurant gift card sales, says around 70% of gift cards are used within six months. But many cards — tens of billions of dollars’ worth — wind up forgotten or otherwise unused. That’s when the life of a gift card gets more complicated, with expiration dates or inactivity fees that can vary by state.

What happens to the billions that go unspent each year?

Here’s what to know about the gift cards you’re giving — or getting: LOVED, BUT LOST After clothing, gift cards will be the most popular present this holiday season. Nearly half of Americans plan to give them, according to the National Retail Federation.

But many will remain unspent. Gift cards get lost or forgotten, or recipients hang on to them for a special occasion. In a July survey, the consumer finance company Bankrate found that 47% of U.S. adults had at least one unspent gift card or voucher with an average value of $187. That’s a total of $23 billion.

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Spirit Airlines admits error and apologizes to family after 6-year-old boards wrong flight.

Asix-year-old boy named Casper found himself hundreds of miles away from his family after being mistakenly placed on the wrong Spirit Airlines flight. The incident occurred on December 21, one of the busiest travel days during the holiday season. Casper’s grandmother, Maria Ramos, had planned to meet her grandson at the airport in Southwest Florida. However, upon reaching their destination, confusion ensued when airline staff informed Ramos that Casper had missed his intended flight.