It sure seems to be what is going on, doesn't it. Popcorn,Soda, Candy will always be the top $$$ makers, but there is room for additional items. You also need to remember that every market is a little different. What may sell great in one location, won't sell at all in another. But, I'm always open to testing new things, and going from there. You need to ask yourself some questions to see if you should continue selling certain items:
Do I sell enough of this item to justify keeping it on the menu?
Does my profit from this item justify keeping it on the menu?
Is selling this item taking away sales from a more profitable item I sell?
Am I spoiling more of this item than I am selling?
Is the prep/work involved making this item slowing down my employees?
Remember proper merchandising of items is extremely important, and may be the cause of a success or failure.
IF i were the average theatre(not a big city art house high $$$ end crowd)I would go with the staples, Popcorn, Soda, Candy-and these additional items,Nachos,Pretzels,Cotton Candy, Sno-Cones--these additional items are easy to prepare,not much to store,and very Profitable. I would dump those expensive juices,and muffins,cookies etc. Too much labor to prepare too much spoilage,not enough sales..
Every market is different...see what works in yours.