My dad loved these! cold or sometimes he would stuff a bun with it and heat it up in the oven, all melt-y.... -Here is what he used:
minced ham (food processor works better than chopping)
grated cheddar cheese
minced onion
chopped hardboiled eggs
Sometimes green olives or pickles or relish
moisten with mayo and a little mustard or Durkees to the consistency you like...