Have a friend who once got more spaghetti than he could eat at a lunch stop, so put it in a baggie in his jersey pocket. Ate it with his fingers during the rest of the ride. Kind of messy. OTOH, we're still talking about it! Both simple and cheap - yesterday's spaghetti. Don't wear gloves.

Panini have a fine pedigree. Make them from most anything, stick in jersey pocket, eat after the climb not before. But really, if you're riding all day, panini are killer. Everything you need.
http://www.squidoo.com/Panini-sandwich-recipes
etc.