I am in charge of purchasing items for a iron-chefish burger cooking contest between friends this weekend. They'll be limited in prep ability - basically, a grill and a knife - and we're not talking about professional chefs here, either.
Standard condiments like ketchup, mustard, etc, will be there already.
So: I can think of some obvious ingredients that are useful if not creative, such as tomatoes, onions, lettuce/greens, and pickles. But I want to get some stuff that'll give them a chance to be more creative, obviously, and I was wondering if anyone had any suggestions?
It could be a suggestion for a particular type of burger you've had, or just for something that you think would be an interesting ingredient for people to try and work into (or on to) burgers.