If you've got a bag of popcorn in the pantry, you're set for snacks. Pop up some popcorn (an air popper or simple microwave popcorn popper makes this easy and cheap - no need to buy overpriced and ickier tasting pre-bagged stuff) and drizzle some olive oil or melted butter over top. A sprinkle of salt, or even parmesan cheese and you're set! It literally only costs pennies a bowl. Stock up on popcorn when it's on sale. Freeze it in a tightly sealed container to keep large bags fresh longer.
Enjoy your frugal snack!