Oh man, you know what I'd pick?
Star Wars Episode IV: A New Hope
Classic movie that probably looks amazing on a big screen that I've only ever seen on a small one. I have never had a bad time watching the original Star Wars. It's just a simple, fun movie that's easy to enjoy.
As my snack, I'd go for an ice lolly. When I was growing up here in the UK, popcorn wasn't a big thing associated with movies, and it was more common to have ice cream or an ice lolly, so that always feels more "right" as a cinema treat for me.