Salsa, fried onions, all types of cheese, saurkraut, diced tomatoes, fried mushrooms, raw onions, chili, guacamoli, bacon....use your imagination!
Personally, I like to dice tomato and onion, mix them together, steam the bun, BBQ the weiner...then add relish, a slice or two of bacon, mozzerella cheese, then the tomato/onion mix.....good eating!

I tried to do most of them at once on a dog but needed a knife and fork and a real big napkin.

Ron