Oh I didn't eat or drink at all. I went to the bathroom before driving out to the theater (35 minutes away), got there 5 minutes early, then went to the bathroom again before sitting down (reserved seats). Didn't feel the need to go until after the credits finished.
It's a good idea to have something to drink during the day, cause you don't want to get dehydrated or your body will respond by filtering your fluids harder, forcing you to pee more (sounds ironic, but that's homeostasis for ya). Just don't overdrink, but don't get too thirsty. If you really want to drink in the theater, wait until when you feel the second act starts.