If you have a big purse, pop a mini bag of low fat popcorn at home and smuggle it in. Otherwise, pack a small granola bar or fresh fruit or whatever your favorite snack is from home - there's very little at the theater that's healthy just because of the portion sizes. Even the Twizzlers - which I thought were a healthier option - have something like 600 calories, so be careful!
As far as i know, other then a bottle of water there is nothing that is healthy at the movies...I have had alot of clients ask me this very question, and threw the research i have found....bring your own. Pop your own 100 cal bag of popcorn, or even find a 100 cal choclate bar for a treat...almonds...fruit, veggies, low calorie hard candy, ganola bars ect..
Do you need to eat anything at a movie theatre? I know, I didn't grow up in North America so the popcorn and soda combo while watching a movie is not engrained in me so deeply as in others. But I make a habit of go to the movies after I had dinner (or another meal) and I don't feel the need to snack.
At Christmas, when I was in the US, we went to see a movie after picking up a few things at Walmart and I was mentally smacking myself senseless for having not purchased some bottled water at Walmart. When we got to the movie theatre I was suddenly thirsty and I got extremely annoyed when they charged me $4.50 for a bottle of plain Asani water (x2, a bottle for each of us). Bloody murder! As a rule, I don't buy anything at a movie theatre so I didn't even know how expensive things got there.
If you MUST snack, why don't you make some trail mix at home (better home-made than the pre-fab purchased one) or bring some almonds or other nuts.