Your passport, possibly a visa (you are a minor). And travel light: a carry-on bag is usually sufficient: what you bring you carry. Bring your music. A mag or two. Pen and paper if you're in the mood to take notes. Your camera.
Always depends on the thickness of your wallet or if you want to "rough it" a bit. Check hostelworld.com for various types of accomodations and rates. Also, cheapest form of travel is by Greyhound bus. Also couchsurfing is a good site to make "connections" and sometimes a free night of lodging...
Ok, so I'm a guy and we pack differently, but I'd say bring as little as possible (whatever will fit in a "carry-on" flightbag). You're not going for ever and there are washing machines over there. So: whatever you're wearing, plus change for possibly three days. An added pair of shoes or...