This is where all good food starts in Philadelphia. Besides the great Amish stands, you can sample the best of what Philadelphia has to offer. I recommend DiNic's for a delicious roast pork sandwich, Termini's bakery for amazing, authentic Italian pastries (get the cannoli!!). The Mexican and Thai restaurant stands are always packed and I haven't had time to wait in line, but am planning a special trip!
For local flavor, take a seat in the Beer Garden and have a cold one. You can sit and have a great meal at the Down Home Diner.
If you are inclined to cook at home, there are amazing fishmongers, butchers and vegetable stands. This is really a treasure trove that is not to be missed.