Snacks!
Get like 35 dollars worth of snickers bars and stuff in the checkout line haha.
You could get a movie, but, its kind of a waste since you probably have a NetFlix subscription, Playstation Network, or something along those lines. I rarely buy movies anymore.
You could spend a bit more and get a video game.
Check and see if its cash redeemable.
If it was me though, I'd go with Exit's suggestion of the CD/DVD cases. They are expensive and I never have enough of them.