I went with Regularly, but I probably tend more towards Often. I am lucky enough to get free screenings quiet often, which slants the following opinions...
Every movie is better on the big screen, and I find that if I am confined to a theater seat I am more likely to pay closer attention to the movie at hand. At home I tend to lose focus every now and then, making the theater experience supreme, especially, as others have said, for the spectacle movies, but also for the group experience. Seeing something and reacting to something is a group, even a group of strangers, is always better than in isolation.
I tend to go to quite a few by myself, though I have a sci/fi comic book buddy I take along to those screenings, and my wife will come sometimes too, but only if it's something she is actively interested in, or if her schedule permits.
I will still go and pay to see some films, even with the ample screenings and access to end of year screeners at home (see above opinions on seeing things in theaters). But not having to pay for the majority of the things I see also permits me the expense of seeing those movies I do pay for. Sometimes I miss screenings, or things aren't screened that I want to see, so I will shell out to see them in theaters.
As for theater food, my wife always wants Red Vines and a soda, or some other snack. I almost never get anything when I am at the theater, but will share a soda with her, and eat some of her candy