Things you should do both tourist and local:
1. Downtown - hit the shops in Union square and if you need some Hip Hop clothing head West on Market near 5th 6th and 7th check out First Step for cool Bay Area shirts, Fits Fashion etc.
2. The Mission - great Mexican at El Farolito and La Tacqueria on Mission 24th or 25th. Many other good spots but those are two of the ones people argue over all the time. If you do El Farolito get the Quesadilla Suiza. Also check out the street murals on 24th and Capp, 24th and Lilac, 24th and Balmy Alley is famous for the artwork. Dont wear colors.
3. Haight St. - the head shops are cool but overpriced. The real cool thing about Haight St. is walking around and people watching. Also Amoeba Records there is one of the biggest music stores I ever seen, tons of good hip hop cheap cds new and used. Golden gate park drop by Hippy Hill and smoke a blunt.
4. North Beach and Broadway. Fun area to hang out at night. Even if you're underage you might be able to sneak into a Bar/restaurant early before the doormen come and get some drinks. Italian food is very good I would reccomend either Tomasso's Pizzera on Kearny/Broadway, Sodini's original on Green and Grant. My personal favorite is Firenze By Night Stockton and Columbus. China town is not too far away either. You could spend a whole day on that side of the city.
5. Viewpoints are twin peaks all the way up market it turns into portola and you make a right on twin peaks follow it all the way up. other side of the Golden Gate Marin has a couple nice views first and second exists after the bridge. Make sure you see the Gate.
6. Cannibus Clubs may or may not serve you no reason to go to 13th and Geary plenty of decent ones on the other side of town.
7. id check out a Giants game especially if youre underage its a great passtime and the stadium atmosphere is cool as fuck.