I'm not sure how this theater is arranged. My local theater serves beer/wine and some heavy snacks. But, it doesn't have table service. Just the typical counter service. I've never tipped and always assumed the counter staff is earning at least minimum wage (no different than buying a latte at Starbucks).
The few times I've gone to a movie theater with table service, the tickets and food/drink were separate bills - tickets purchased in advance of the showing and food/drink ordered during previews/ads. The food bill would be tipped like any other restaurant with table service.