http://www.wawa.com/

Wawa's a Philadelphia institution. You can get standard deli sandwiches and a Wawa specialties at any of these (along with the usual convenience store fare) and most are open 24 hours. The ZIP for PHL is 19153, though if you're cabbing from the airport the driver will likely know where the nearest Wawa is.

If you change your mind and decide to get a hotel on the Main Line, there's Minella's Diner in St. David's.