When we were kids, we ate mayonnaise sandwiches - mayonnaise (Hellmann's, never anything else) on white bread. Usually, but not always, with lettuce and a sprinkling of salt.
After-Thanksgiving turkey sandwiches were turkey, a generous spread of mayonnaise, lettuce, salt. If I had turkey in the fridge year-round, I could probably eat one of these every day.
My favorite ham sandwich is ham with a good swiss cheese. Spread mustard on one slice of bread (or better, a good semi-hard roll) and on the other side spread mayonnaise. The ham goes on the mustard side, swiss on the mayo side, never the other way around.
We have a local sandwich shop that offers what is essentially an Italian sub - salami, pepperoni, ham and provolone, with lettuce, tomato and onion. They put oil & vinegar on it, but for some unknown reason, unless you ask them to hold it, also mayonnaise. Who in the world puts mayonnaise on an Italian sub?