Late Night in Philadelphia
Lots of places in Chinatown are open late, but I don't know any specifics.
Lots of good bar food abound. Standard Tap (2nd & Poplar) has great food and beer in a casual atmosphere. Interesting in that the menu is entirely on a terse chalkboard that obscures high level dishes. For example, "Duck Salad" is a salad with duck confit that is considered some of the best in the city. I got a "Mixed Grill" that turned out to be venison sausage, elk steak, and venison steak (and it was great). Also has a great burger and bar food. Only serves local beers on tap so if you're from out of the area, that's fun as well. About a 10 minute drive from CC. Their sister restaurant is Johnny Brenda's (a bit farther) and just as good.
Many of the taquerias in South Philly are open til midnight or later and can be interesting in their authenticity but lack a lot atmosphere. Nearly all are BYO. Taqueria Veracruzana is great but I'm not sure how late they are open.
You might consider Melrose Diner or Oregon Diner in South Philly. Neither have outstanding food, but are classic diners with atmosphere and service stuck in the 1950s.
Other good late night kitchens: Pub & Kitchen, Silk City, North Third, Royal Tavern, Cantina Los Caballitos, Cantina Dos Segundo.
i am all about the chinatown dinners after 11 pm. shiao lan kung used to be open super late all the time, but i am not sure what time they close now. they are definitely worth investigating. barryg's taqueria and gastropub suggestions are definitely good ones too. i would agree with any of his suggestions except for the two cantinas. the food there is very meh.
I'd stick to the bars. A lot of bars in Philly serve good food, usually until midnight. I'd second Standard Tap, Pub & Kitchen, Silk City, Royal Tavern, and add: Good Dog, St. Stephen's Green, Monk's (if you can put up with the crowd), and Shouk.
In terms of Chinatown, I can't see a thread like this and not recommend the fried pork dumplings at Davids. My mouth waters just thinking about them, and that delicious grated ginger dip. They also have great mei fun.
David's also sells beer to go. So you can grab a 6 pack on your way back to your hotel/ house.