E.
Wouldn't rice krispie treats fit the bill? Those just have rice krispies, marshmallows and butter. Also, as I recall from another class at my preschool, a girl with those allergies almost always has a steady supply of Oreos. Maybe you could check the labels on those.
Or you could get ahold of the child's mom and ask her what treats she gives him. But from my experience, kids with allergies are used to having special snacks at school. So it might not be that big a deal to him. Still, it is sweet of you to be so thoughtful!