Most Likely: Nothing will happen. Your half-finished bottle of mineral water or bag of homemade brownies won't get you booted, and you won't have to fork over a small fortune for concessions. "Nothing really bothers us unless it's smelly, alcoholic, or slippery if left on the floor," says Steve Gaines, a manager for City Cinemas, in New York City.

Worst Case: Humiliation. An usher may ask you to eat your food outside the theater. Moviegoers who refuse to give up their snacks could be asked to leave, but their money will be refunded.