You are experiencing classical conditioning. A neutral stimulus (the movies) was repeatedly paired with a response (eating candy and popcorn), and so now the two are linked.  Since eating is pleasurable, you feel unhappy when the food is taken away. To break the stimulus-response chain, develop a plan before you get to the theater. You could neglect to bring cash for snacks, or go to the movies with friends who don’t snack, or you could bring a healthy snack from home. It helps to commit to eating (and not eating) according to your hunger signals, and so if you are not hungry, please don't eat, but if you are hungry and you elect to eat popcorn, then buy a small size, skip the extra butter, and enjoy!