I'm not someone who goes to the movie theater very often. I really have to be interested in seeing a particular movie to drag myself out to the theater to watch something. I do enjoy the movie theater experience, but there are numerous factors against it being a norm for me. I'm open to all genres but my particular interests are narrow, which limits the scope of things that I'd want to spend money on a movie ticket on. Related, I'm in no rush to watch most movies and am perfectly content to wait however many months it takes for movies to release on physical media (DVDs/Blu-Rays) that I can rent from the library or watch via streaming services, both of which give the freedom to watch from the comfort of my own home. I'd rather be frugal and practical with my money and limit unnecessary expenditures like going to the theater unless, again, it's something that begs the experience.
With all of that stated and out of the way, on the occasions I would go to the theater in the past, I'd say my go-to snack was Nestlé Buncha Crunch. Crisped rice chocolate is nice and the individual pieces were preferable over an ordinary Crunch bar. However, for numerous reasons, I'm not particularly interested in giving them money. So I'd probably have to figure out a different option or just go without.
At home, though, if it's a movie I'm really interested in? Gotta be pizza, haha. Obviously not every time, of course, but yeah.
Most theaters don't mind you bringing your own snack usually. The theater I worked for allowed it for all customers. I just make a stop at dollar tree or someplace if I want something for a theater. I think most people do movies at home anymore since 2020 and because streaming services are so big.
Depends on the individual theater and the individual management of said theater. Some places will let things slide if you don't make it obvious, some places will think it's more trouble than it's worth and don't want to risk goodwill, some have an outright ban and want you to only buy from their concession stand. A drive-in theater around here has a penalty for people bringing food in and a pass you can buy to permit you to do so, as concessions sales are how they stay in business.