The theater I used to work at was never that strict about bringing in food. If you made it obvious you were bringing in food we would ask you to throw it away, or finish it before entering. We would never search someones bag, or throw someone out that we didn't catch on the way in. For the most part people sneaking in food were the type of people that would never pay the crazy food costs at a movie theater anyways, so it was always better for use to keep customers happy.

We were much stricter about people sneaking in camera equipment though. In fact if an employee caught someone trying to record a movie the MPAA would pay you a $5,000 reward, and our theater would match that with another $5,000.