for historical/touristy shit:
hit up the liberty bell, constitution center, independence hall, old city and all that
for philly eats:
It's cliche, but i guess mandatory, you gotta either go to Geno's or Pat's and get a cheesesteak, although I subscribe to the Dalessandro's school of thought when it comes to cheesesteaks.
Tony Luke's has awesome sandwiches like roast pork or chicken cutlet italian. I like either one with broccoli rabe and sharp provolone
Primo's Hoagies in south philly are the best hoagies, but some Amoroso worshiping bitches don't like their rolls.
There are some good bars in old city or manayunk, although the manayunk ones tend to fill up with fun-boys and yuppie whores.