Snacks for a film are hard, because you yah munch without thinking!
Savoury snacks - salsa with carrots, peppers, cucumber to dip in, or tzatziki
Sweet - hot chocolate (options or similar, with a few mini marshmallows in, or jellly (low fat), if you make it with less water and mix in some fruit, then you can sort of slice it up like sweets!
Tinned pears drained (in juice, not syrup) with a blob of natural Greek yoghurt and a grating of good dark chocolate is delicious too, and a good cupboard standby too!
Frozen fruit and natural yoghurt, blended, makes instant healthy 'icecream', and you're getting more fruit too.
Don't buy chocolate, crisps etc, therefore if it's not on the house then you can't eat it!