I'm sure I'm taking us off on a tangent, but being a Philly native, I have to. Cheesesteaks with whiz are kind of gross, and really something you only see at places aimed at tourists and drunks - Pat's and Geno's being the most well known (even though they'll do other cheeses, and it's not seen as strange). It's certainly debated and plenty of folks in the area like whiz, but that's my take on it. For me the classic growing up was a cheesesteak with provolone and onions. Real cheese for sure. Don't get me wrong, I've had plenty of them with cheez whiz after a night of drinking, but to me that's not the real deal.

I suspect whiz caught on because you could open a giant can of it, keep it warm on the flat top all day, and quickly apply it as needed. And before you break the can, who knows how long it's shelf stable - I'd lean toward indefinitely.