There are basically 3 options for food at your Prom; a sit down dinner, buffet style, or pass arounds. The facility you choose will usually have set menus from which you may choose. They will make minor changes for you if you like, but for the most part you choose from their menus prepared specifically for high school proms. (Ask about special diet situations, such as, vegetarian.)
The smartest option is usually a buffet, because most students don't eat much & it gives your guests more time to dance. If a hall does not execute a sit down meal properly it could take up to an hour for them to serve everybody! We have seen it happen especially when halls are understaffed and have crowds over 300, where half the room is done eating and the other half is not even served yet! This puts quite a damper on a prom because the half that finished wants to dance but the catering staff will not let the DJ open the dance floor until everyone has been fed!
Your student committee will usually have pretty strong opinions as to what they want, so let them choose, as long as they stay within the budget. You will find that at most places the difference between the cost of a sit down dinner and finger foods is small, so you might as well go with the sit down dinner or buffet.
Note: If you do pick a Buffet Have your DJ call 3 or 4 tables up at a time so that it stays under control. If you have any meal have the DJ play the rock and other non-danceable requests during that time. Also if your photographer needs table photos dinner is a great time to announce them (the 1/2 that has not been served food yet!!)
Unlimited soda should be included in your price as well as dessert. Don't be afraid to negotiate. You are the representative for your school, and facilities expect you to ask lots of questions so that you get what you want.