My sister has thrown a Halloween party every year for the past ten years, and she's pretty good at making interesting snacks, or making snacks interesting.
Not sure of the recipe, but each year she makes crackers or cookies in the shapes of bones. Also, if you cut a little snip off of a hotdog, dab some ketchup on there and add an onion "fingernail", you can make convincing lumberjack's fingers.
A lot of it is just changing the names of things. Try putting little signs with odd names over stuff. Green kool aid? No. That's troll blood!
Edit: Prizes for costumes is another decent idea.
*Actually, those parties have been pretty booze-oriented. So I guess I can't suggest everything that happens there.
