What you should do to stay awake throughout the entire movie is to drink something cold preferably an energy drink or soda. Keep your mind occupied throughout the entire movie by eating snacks. The action of chewing will help in keeping the brain active. Make sure to sit up straight.
lots of caffiene, and possibly a quick nap before u go if your really tired. plus go to see a movie that u r interested in! wanting to b awake to watch it will go a long way toward keeping yourself awake!
DO NOT DRINK A ENERGY DRINK...they are HORRIBLE for your health. If you start to feel sleepy eat something crunchy (not to loud) or review times tables in your head. If you really start to feel sleepy excuse yourself and splash water in your face or shake your head really hard.