I agree that your District's nutrition services is a good source. We purchased a couple things through them for a breakfast we did earlier this year and found the prices they have access to are WAY lower than even Costco/Sam's Club/WalMart. You might want to see what they can do for you.
I'm a big fan of Sam's Club for things like this. I buy a lot from them for our school to sell at various events. It isn't a huge money raiser, but it's easy enough to figure out how much each bag costs you, and then figure out how much to sell them for so you make your money back, plus some extra.
Does anyone know of a compnay where you can purchase cheap bagged snacks? We use these for various school events (bingo night, festival etc..) and it would be nice to have a source when donations are scarce.
