Personally, I don't like doing it. When I am in the cinema, I try to concentrate really hard with what I am watching. I avoid any destruction like the hassle of eating and crunching a pop corn, getting to the toilet to pee and wash my hands. I hate all these kinds of disturbances. I want all my attention to be directed to the movie I am watching.
I use to eat popcorn while looking at a movie but the cost of the movie tickets has gone up so and the cost of the popcorn makes me think the popcorn is made out of gold, so I stopped eating popcorn when at the movies.
What's funny is that I usually buy the popcorn and drinks and then go sit to watch the movie. I snack on them during the advertisements and when the actual movie begins I just sit there and sip away at my drink if I'm thirsty. I can't stand the noise in my mouth when I'm crunching on the popcorn. If I'm extremely hungry then I'll take some more but other than that, I don't really snack on it DURING the movie xD
I usually only snack during the commercials and the very beginning of the movie, if I'm seeing something in a theater at all. I generally only take a packet of gummy worms and a bottle of water with me, so there's not much for me to munch on anyways. I don't really like going to the theaters anyway, asides from the obvious really expensive ticket prices that I can't afford, I also don't like being stuck in a seat for 2 hours. I like watching stuff on my computer or the TV, so I can pause it and get up and walk around or whatever. I get twitchy if I sit for more then like, half an hour or so.
I will usually get a Diet Coke and popcorn. I don't vary a lot from that. Eventually I'll get some junk food like chocolate and candy.... but usually not. I have taken mixed nuts before, and that is also a great snack for the movies! But I never remember to take it with me to the movies, and to buy it there is way more expensive.
I do get into this mood sometimes, but it depends on the movie. If the movie is just a simple action or comedy movie, then I do enjoy snacking on small items because I don't feel like I need to be immersed in the tone of the movie or concentrate too much, but when it comes to serious stories then I may be a bit more hesitant to snack and more likely I'd just want to concentrate.