In CT, mustard and sweet relish, mustand and sauerkraut,mustard and dill relish, chili and cheese, ketchup only, cheese only, and onions can be found on any of these.
While we lived in VT, sometimes you would see a hotdog like in Eastern Township, Quebec-very finely cut coleslaw with a vinegary dressing with mustard. This is excellent, and I make it at home sometimes.