While I'm partial to Pumpkin Juice, Butterbeer I think is the best value as it's $7. Which is a lot of money compared to other snacks. Another thing would be the big Lard Lad Donut which is about the same price and can be a snack for the whole family.
I do not have the full list of items as USF or IoA, maybe someone else does. However, it's typically anything you can think of that would be considered a snack, typically sweets, but things such as pretzels obviously would be a snack as well. Essentially anything that isn't a meal, or considered an entree (a slice of pizza is considered an entree for example). I heard the turkey leg doesn't count however.