This one is–you’ll be shocked–from college. I was going to school on the Main Line near Philadelphia, and there was a 24-hour WaWa with a grill.
We came up with: warm roast beef with pepperoni cheese*, grilled onions, mustard and horseradish on a kaiser roll. As my mother might say, "It’s one of those things it’s a miracle we survived."
*This was processed American cheese with bits of pepperoni in it. When the heat from the beef and onions softened it up, it was transcendent.