The farmland to the east and west of Philadelphia produces the best meats, milk, and produce on the United States' East Coast - which plays a major part in Philadelphia's large number of fine restaurants. Fitting for a city as justly famous for its plebian as its patrician culture, it's also home to some of America's most unique (and fattening) regional cuisine.
If you're on Atkins (or any other sort of diet, for that matter), you may want to stop reading here, but if you don't mind putting on a bit of weight, here are some suggestions regarding how to do so enjoyably. Besides, Philadelphia's eminently walkable streets allow you limitless opportunities to burn it off...
Food carts: Most American cities have these seemingly unsanitary institutions, but none can match Philadelphia's for their quality, density, variety, and (perhaps most importantly!) hygiene. As the fast casual trend has raised the prices (and expectations) at the city's sandwich shops and lunch counters, these humble vehicles dish out huge quantities of tasty fare that will almost always leave you change from a $5 bill. The largest concentrations are in Center City (particularly around City Hall), across from 30th Street Station, and at strategic points near the University of Pennsylvania campus.
My personal favorite is Pong Yee, a marvelous Chinese institution that puts its four-walled competitors to shame in terms of price and quality, although certainly not service. It's best to call your order into (610) 812-7189; otherwise, you'll have to wait 15-20 minutes for the food to be prepared - all dishes are made to order. The Singapore noodles, beef with broccoli, and "pork billy" specialty of the house are all winners - it's located next to the University of Pennsylvania's renowned Wharton School at 38th and Spruce Streets. It's open 11am-9pm Monday to Saturday.
Also outstanding (and a bit closer to Penn's Museum of Archaeology and Anthropology, which is the main draw for casual visitors to West Philadelphia) is Magic Carpet Foods - a vegetarian lunch truck which nevertheless draws confirmed carnivores like me for its superb seitan and flavorful falafel. The lengthy line at noon testifies to its popularity, but it moves very quickly. In particular, the Belladonna wrap and falafel salad (be sure to ask for lots of tahini on top) are outstanding and ridiculously inexpensive. It's located at 34th and Walnut, the northeast corner of Penn's undrgraduate campus. Note that it's only open 11am-3pm on weekdays.
Hoagies: A cynic (which many people will tell you is simply a synonym for Philadelphian) might tell you that the only thing that distinguishes these flavorful sandwiches from Boston's subs or New York's heros is their city of provenance. But there's something much tastier about these homages to traditional Italian lunchmeat and fresh vegetables (you won't find any bologna inside in any sense of the word!), which take their name from Philadelphia's Hog Island shipyard, where workers first enjoyed them. I'd personally argue that the freshness of the Delaware Valley's superb farm products explain their superiority to their Northern cousins, although others credit the subtler blend of spices employed than in Boston or New York. Betraying my recent arrival to Philadelphia, I'm still sufficiently seduced by their overall quality that I haven't yet found a single favorite hoagie shop. Wherever you order one, I am told by native Philadelphians that they're best enjoyed with a light Italian dressing, which brings out the flavor in their vegetable components.
Wawa: You might think that in listing a chain of convenience stores as one of Philadelphia's culinary traditions, I'm illustrating either the city's charmlessness or my own ignorance, but I can certainly assure you it's not the former. Wawa, an offshoot of the dairy company of the same name, offers surprisingly inexpensive and fresh food and the best produce you'll ever see at a store of its kind. In particular, their computerized hoagie ordering system is a joy matched only by the relatively reasonable price for these tasty sandwiches. On any jaunt through the city, you're sure to see people drinking from their trademark square liter bottles of various beverages - their iced tea and chocolate milk really deserve to be distributed nationwide!
Scrapple: I'll be honest, I find the concept of "cornmeal mush made with the meat and broth of pork, seasoned with onions, spices and herbs and shaped into loaves for slicing and frying" (the dictionary definition of scrapple) a tad off-putting. Nevertheless, as your faithful Philadelphia correspondent, it's my duty to inform you of this apparently delectable dish, developed by Pennsylvania Germans in the east of the state and then popularized throughout the northeast as a result of its Philadelphian renown. True conoisseurs apparently enjoy the fried loaves dipped in maple syrup, which my mother claims I did as a child. (I disclaim all knowledge of such consumption.) At least, she tells me that I consumed it "raw" (as opposed to fried), which is perfectly safe, as the pork has already been cooked. (Although the concept of safety is perhaps in the eye of the beholder in this case!)
Cheesesteaks: By contrast, I'll freely admit to consuming a cheesesteak at none other than Pat's Steaks, the self-proclaimed originator of the sandwich synonymous with Philadelphia. If you're willing to make the journey through South Philadelphia (Rocky's neighborhood) on foot, it's certainly a just reward. However, if you follow my lazy example and take a cab to its bare-bones location at the intersection of 9th Street and Wharton and Passayunk Avenue, you'll be punished for your indolence by a sensation of bloating almost as soon as you've finished wiping the sandwich's residue from your mouth, hands, and clothing (and you will have to do this!) While some claim that Geno's, located somewhat more salubriously inside a McDonald's-style shelter (Pat's resembles a stadium concession stand) catercorner to Pat's, is superior to its predecessor, its self-proclaimed "authenticity" (and higher prices) suggest that it is in fact struggling to truly possess this quality. In any case, I've never been tempted to try it.
Regardless of where you order your sandwich, it's important to learn cheesesteak etiquette (yes, there is such a thing!). You should decide beforehand what you'd like to order, as a single error will make Philadelphia's countermen belie the city's otherwise justified reputation for friendliness. As for the order itself, first state the sort of sandwich you'd like (pepper, plain, and pizza steaks are just what they sound like). But you should never ask for a "cheesesteak." Rather, state "American", "Provolone," or "Whiz" (the choice of connoisseurs - yes, as in Cheez Whiz), and do not repeat John Kerry's ignorant error of stating "Swiss" unless you're in the mood for public humiliation. Then state either "wit" or "wit-out" depending on whether you'd like onions. Personally, I'd recommend "American wit" and then topping it with complimentary hot peppers, but "Whiz wit" is the most authentic order.
There's no better way to round out any Philadelphia fast-food meal than by purchasing a water ice, a combination between a slightly more flavorful slurpee and a fruit sorbet, which is most delicious (and filling) if ordered with frozen custard mixed in. Rita's is the most widespread purveyor of this particular delight.