Better than small sweet popcorn! What cinema are you going to? I think they vary from cinema, to cinema...
Blockbuster cinemas (do they still exist?!): Small Salted: 397cal/100g, 99cal/25g serving
Vue: Large Salted (I couldn't find any for small) 459cal/220g serving
And I couldn't find any for Odoen.
Alternatively, you could stop off and get a fruit salad or some fruit to take with you?