This depends on the teens. Girls may be polite and drink the soda like its going out of style while the boys will devour pizzas and chips. For a teenage crowd, and I have experience in this, to be on the conservative side of things, I would go with 3-4 people per pizza (beware the pigs) and 4 people to the larger bags of chips (pick what you like -- if it's left over, you get to eat them). If you are thinking you may go overboard, you could go to a wholesale store and get the variety chip bag boxes of individual bags. That way you will have a lot of variety and the teens will only take what they need and whatever is left is yours for school lunches and munchies. As for soda, I would go with what others suggested and figure on 2-3 per bottle. On this one, limit variety. Get one regular and one diet type of soda. You are not going to please everybody. For instance coke and diet coke. Also, get some water bottles. You can get a case in the market sometimes for $3 on sale.