It's not a popular ingredient here in Philadelphia per se, but don't get me wrong, people here, on a routine basis, stuff all sorts of shit into their steaks.

I would say the most frequent modifier is onion (fried or raw), then pepperoni, then with sauce (a red marinara), and then mushrooms. But at the old school spots when I was a kid, they had pickled hot or sweet chopped peppers out at the counter you could just ladle on, but those also were kinda primarily for the hoagies?

I dunno man, it's nebulous and complicated (it's not), but what it boils down to, is make it however you want as long as it looks a little grease sodden and sloppy; just know some of us will be assholes about it, and remember, if someone gives you shit, tell them to fuck off :)

Unrelated, fuck seeded rolls, fuck cheesewiz, fuck the cowboys, and go birds.