I always liked the flying suit that Ruka (the mad scientist character in
Tenshi ni Narumon) invented for Noelle that uses intestinal gases to fuel an internal motor that makes the wings flap.
http://sensei.rubberslug.com/gallery/in ... emID=86030
It really does work! And, even more interestingly, the primary gas generated internally after consuming partially cooked sweet potatoes is hydrogen, not methane, and so it does not contribute to global warming. I understand that there is serious research taking place in the Pacific Belt to replicate intestinal conditions to generate commercially viable supplies of hydrogen from fermenting sweet potato mash.
I like gadgets that work in both this world and in lala land.