The trick is to use one tortilla, pile on your ingredients, fold it almost like a burrito, and wrap it in foil. Then stick the foil packet on the grate, and let the it cook until the cheese is melty and the tortilla slightly crisp.
Make a s'mores box to store all of your supplies! Duh.... So annoying to juggle the pack of crackers, the sticky bag of marshmallows, the candy bar... It won't change the world, but it will simplify my camping!