I am with the sneaking in snacks to the cinema. Our last movie we popped into we didn't bring anything though and that wasn't too bothersome. We hit up Taco Bell afterwards.
As a vegan, Taco Bell has been one of my better bets as they are always ready and willing to veganize anything for me and some of their dishes are already vegan.
I am at a ditto with the pizza thing. Just inquire about the dough and get it without cheese. I always had pizza like this even before I went veg*an and it's delish! Mmm ... [I'm a a mushroom fanatic so I never cared about the rest of the pizza anyway ... the rest was just filler ...
].
Buffets tend to not yield much except fruits and maybe some steamed veggies.
Some Italian restaurants can yield some good results as well, such as Olive Garden. Their Minestrone is vegan as well as their salad and I always get the Capellini Pomodoro when I go there. It's already vegan and it's phenomenal. Based on their website they use Olive Oil to cook, not butter.
Macaroni Grill isn't as good because even though cheese is not listed in the ingredients of the pastas they top every single pasta dish with it without warning you and for me it was an extremely unpleasant surprise. I haven't gone back but if you know before you go you can at least remember to ask that the dish not have cheese on it.
Any sort of Ethiopian restaurant will have good dishes as well. I love Stir Crazy, because I can have tofu substitued in any dish and the menu tells you what's vegan what isn't right down to the sauces they use [it lists each sauce right on the menu and tells you which are "true vegetarian", which is SO nice].
Japanese/Asian restuarants are usually good bets as well. I had a Japanese Tofu Soup once that was yummy.
Just look around and explore your options.