Kanka rocks for really bad sores in inconvenient places. There is also something called Glyoxide (drugstores often have a generic version for less $$) that works for the not as bad ones. If you like self-torture you can always use plain old hydrogen peroxide (with these last 2, be sure to spit them out).
Also, whiskey helps, at least it does mine.
Stay away from ketchup and acidy things, they hurt!