Mustard is actually a hypothetically acceptable alternative to mayo per a meatloaf sandwich. The vast majority of physicists agree on this. What kind of mustard, and is the meatloaf hot or cold? Toasted or not?
Freegards
Leftover meatloaf, cold, on fresh white bread. Any kind of mustard, but spicy brown is nice.
Now, leftover turkey offers many possibilities...leftover turkey sandwiches are the best part of Thanksgiving dinner - especially if you’re the one who slaved over the meal :-)
Cold meatloaf on white bread with catsup.