Onions. Lots and lots of diced, fried onions. Then ketchup and mustard. It's weird, I hate American mustard, has to be English for me, it's so much stronger and really a different condiment altogether, EXCEPT for on hotdogs, where only American mustard will do.
On a burger: lettuce, red onion, beef tomato, emmental cheese, onion rings, a hash brown, jalapenos, guacamole, a bit of salsa or relish, and maybe a slice of pineapple and some peri peri sauce, depends how I'm feeling. Oh and the burger somewhere in there...