Hey Becca - I went yesterday and I took along a pack of cherries (those plastic punnets from Tescos) and also a pack of that ready chopped melon (I think it's called 'Melon Medley Madness' or some nonsense, from M&S but you can get them in Tesco too).
Grapes are good too - you want something easy to stow away and something like popcorn that you can shove in your mouth all the way through the film!
What are you going to see? I saw The Road yesterday, and it was absolutely phenomenal. I mean I would pay to watch Viggo read the phonebook, but The Road is really something special.
Have fun!
Rx