The most I have snuck in was a small bag of candies in a coat pcoket. But I still bought popcorn and a drink.
I once saw this man in theater who had a can of Diet Coke, bag of microwave popcorn and bag of candy which he pulled out of a backpack. I thought it was funny. Oh I forgot I went to movies with someone once who brought in a two pound bag of Red Vines.
Anyone else's theater sell more than just snacks? The one here sells hot dogs, mini pizzas, nachos, ice cream, ICEEs, warm just baked cookies in 3 flavors, hot pretzels, Italian sodas, plus the usual candy assortments and popcorn. At one time they had hamburgers. I'm glad they stopped those because I hated smelling onions while I watched a film.