Following the topic of "must haves" rather than giving a recipe:

Miracle Whip (O.K., so shoot me!)[:p]
neatly sliced green pimento-stuffed olives (no "salad olives")
celery salt
dry mustard
chopped white onion
sliced boiled eggs
paprika
serve very cold

I like bacon (in potato salad)only in the German variety which is properly served warm.