One person's bad film might be another person's classic (everyone pays to watch) so definitely no mobile/cell phone usage (unless in emergency situations like Warb said).

I too eat at and drink in the cinema but If it's a bag I split it up on side and cup it in my hand so reducing the noise caused by fishing the contents out and I eat with my mouth shut and chew slowly.

Experience has taught me never again get drinks from the cinema (especially those oversized buckets with noisy straws in).

If it can't fit in my pocket I won't consume it and if it can I get it out before the lights go down (oh matron!).