Since you said Friday "night" and not afternoon, I will not suggest taking a taxi to the historic district (Independence Hall, Liberty Bell, etc are about a 20 minute / $20 cab ride away). [As a political science major, this might have been of interest to you.] You could take a taxi to "South Street" where there are a lot of shops and pubs, but, with a 3 hour layover, you wouldn't have much time. I will limit my suggestions to within the airport.
Between terminals B & C is a shopping center with shops and restaurants. Included in that area is a Dock Street Brewery & Pub and a TGI Fridays. Down both terminals B & C are Philly Rock restaurants and bars. I mention all these places because you can sit down, have a drink (being a third year student, I am assuming you are 21 years old) and watch sports on television.
The best restaurant in the terminals, however, is in the Marriott which is at the end of the Terminal B walkway to parking and luggage pick-up (stay on the upper level).
Also, in the connector between Terminal A and B is a "Laptop Lane" if you have your laptop with you and want to do some web surfing. If you want programs or supplies, there is a "Staples Express" at the entrance to Terminal B. If you are into art, there are rotating art collections throughout the terminals. Finally, large white rocking chairs have been added in many locations between Terminals B & C if you just want to rock and watch the people or planes.
For watching the airplanes, the best place is the US Airways club on the third floor between terminals B & C. You might want to see if any of your friends belong or have the one-time passes they give their frequent flyers. [Might even check with whomever you sit next to while flying into PHL. If they belong, they could get you past the front desk as their guest and then leave.]
I would suggest that you go to the following website for the Philadelphia airport and select "Philadelphia Marketplace" to see listings of shops and restaurants by location. It also has a map of all the terminals.
Hope this helps.