Yes, that's right, I'm a cereal killer. (I'll probably carry it in, get chuckles for the first few minutes if I'm lucky, and then put it down and not care about it for the rest of the party. Not exactly a crowd that will care much about costumes anyway, I'd wager.)
Made the knife out of foil and scotch tape, with a note card for structural integrity, in about 5 minutes. Found the cereal in the cabinet, which is probably rather stale anyway, as we don't eat cereal much.