Who decides the order of pairs? (details inside)

I was at a fair on Saturday, and as I was walking through the flea market section I saw a sign that said “Bolts and Nuts”. That got me thinking, when you think of a pair of something, why does a certain order sound right? There are quite a lot of pairs like this:
Bacon & eggs
Salt & pepper
Ketchup & mustard
Pickles & ice cream (I still haven’t figured out who would eat that!)
Burgers & fries

Who or what decides it? Just tradition?