If you are worried about revenge because you are a "difficult customer," then there's really no need to be. If you were difficult, you wouldn't be letting them perform the search or confiscate your gooRAB and they'd have no chance to spike your drink.
If you are allowing them to take your bottle away for the duration of the film, you've been co-operative and they have little to take revenge on.
I posted about this earlier in the thread. Cinemas make very little out of ticket sales. Most of their revenue comes from the sale of food and drinks. To sell food and drinks means they have to have a license and consequently, it will be listed as a part of their business.
As I said before, this is something that would need to be tested in the courts to see if it holRAB up and would undoubtedly come down to the company's terms and conditions, business model, finances, etc to determine whether or not "don't bring in consumables" are fair contract terms.
It's a lot more complicated than "I went there to watch a film, therefore they're not in the food business." Clearly, they are.