Ding! Ding! Ding! That’s what I add to mine when I want to deluxe it up. In a pinch, if I don’t have apples, I’ll add a dollop of apple butter to it.I’m not a huge grilled cheese fan to be honest, but when my dad makes them at the cottage, he adds sauteed onions, sliced apple, and uses smoked cheddar. They are pretty good.