Food Fight!!!

I have found myself in a place I didn't want to be. Not a terrible thing, I just feel very unqualified. I am in charge of the spring fundraiser at my children's elementary school. We are having a carnival with games & a silent auction as well.
We have decided to have a specific activity at the carnival for fundraising purposes that should prove to be very popular. An organized food fight. I'm excited about it, I think it will be a lot of fun. We have the location secured, but here is the question of the week:
In an environment like we find ourselves in these days, what kind of items are appropriate for a "food fight?" Expired food items? "Faux" food items?
We want to have fun, raise funds for our school, but we don't want to be wasteful or provide an example of wastefulness.
Any ideas, gentle readers?