We featured a couple really short articles on cooking on one's exhaust manifold and engine bay in a couple of the first few issues of JPFreek including Tacos al Rubicon, a taco variety cooked on the engine core. I'm drooling just thinking about them.
And, if you really want to be efficient I would suggest our Tortilla Napkin suggestion as you can carry tortillas with you, use them in place of napkins to wipe your hands from eating, and then eat them afterwards without having to worry about additional trash to carry out.