I really think so many of these things in our lives are habits...
Like when I used to smoke, I couldn't IMAGINE there would be a time when I would never think about cigarettes again. 12 years later, it's laughable and horrifying to even imagine that I ever smoked.
Same with night snacking - I used to always have something in the evening after dinner. When I first stopped doing that, it really felt like there was something missing. I substituted herbal tea, which didn't feel as satisfying for a couple of weeks. Now I can't imagine eating something before bed - my habits have done a 180.
Luckily for me, theatre junk was never my habit. DH and I have 3 kids on one salary, so have had to be a little prudent with money for 10 years now or so. I could never stand paying $10 for a drink and popcorn to share... ridiculous. So we just don't, and to behonest, I don't even think about it. Even when I hear rustling and munching all around me.
Trust me, after you've switched your habits for a few movies, you won't ever think about the (insert junk) again!