LIFE:
DON'T GO TO NORTH PHILLY
DON'T GO TO WEST PHILLY
(I thought that needed to be emphasized
FOOD:
Go and try some sandwiches (Hoagies and Cheesesteaks), at some recommended places (like Jim's, which was seconded).
Should avoid the tourist trap places.
Try to check millerjm2's suggestion (Pizzeria Rustica) if you like Pizza (I do), or Beat's suggestion (Tampopo) for japanese
Try Donuts+ for cheap donuts and snacks
NIGHT (I'll personally pass on the "night time" suggestions, but for others):
check crackoaf's bar hopping tips, particularly if you are into beer;
check PhilExile's detailed insight if you are into "panty peeling" (I didn't know the expression, but it is easy to guess);
if you want a girl delivering you cookies*, try Insomnia cookies (and, I guess, hope that you don't have a guy delivering?
People definitively focused on food tips here
*Do not confuse with cooties