The Hard Rock Cafe is right near the Marriott, come out the front doors and look for the large guitar. You might try looking in the Reading Terminal, lots of stands but great food. They have lots of Philly specialties (cheesesteaks and hoagies) as well as food from the Amish in Lancaster.
Chinatown is located nearby on 10th St and Race. (walked to 10th and hang a left)
Lots of restaurants are down between Front (1st) and 7th Streets on Market and Chestnut streets.
(Chestnut is one block south from your hotel)
You may also want to check with Concierge at the hotel.