What does or doesn't go on a hamburger?

With BBQ season coming up, what do you like or don't like on hamburgers (if you eat them, or a vegetable based equivalent)

Bacon
Mayo
Ketchup
Mustard
Pickles
Blue Cheese
Onion
Potato chips
Hot Sauce
Mushrooms

Anything else?

There's very little that I don't like on a hamburger.

I've had everything on the list above voluntarily, multiple times, in various combinations.

Re: What does or doesn't go on a hamburger?

My burger is :

cheddar
avocado
pickles
lettuce
tomato
onion
bacon
either ketchup or thousand island

and I like it cooked medium.