Bring the hassy and one lens. It will save you from getting analysis paralysis when shooting. If you go to the Golden Gate bridge, do be aware that in the early morning it will be shrouded in fog. If you are not renting a car and driving, going over to the Marin Headlands side (although incredibly beautiful and interesting - there are some WW-1 through Cold War fortifications on the Marin headlands that you can explore), it will probably be too time-consuming to cross the Golden Gate Bridge. For something interesting to do on the city side, if you take Geary Boulevard all the way to the end, just before it drops down the hill to the Pacific and becomes Route 1, there is Cliff House and the ruins of the Sutro Baths. Cliff House has a room-sized camera obscura, and if memory is accurate, a museum of old arcade equipment. You can go down the cliff to explore the ruins of the Sutro Baths, and walk on the beach to see Seal Rock. Back up at the top of the cliffs, there is a trail that leads out of the parking lot and follows the cliff heads along the Pacific. Follow that trail along for about a mile and you'll find some stairs down to the beach. The stairs will be on your left, a bit after the Coastal Trail overlook. I was looking to see if I had any images still posted here from the location I'm talking about but I don't. Back in the city, if you're in Union Square, there's tons to see around it if you're looking for streetscapes/people.
You're not far from the Chinatown Arch and Chinatown proper - if you want some interesting street/people photos at the end of the day, there's the outdoor night market (ask around as to where it is located - it's been 20+years since I went to it so I don't recall exactly).
You can grab the street car (NOT the cable car - different animal) that runs up Market Street from the Embarcadero and the Ferry Building all the way out to Castro Street to get a real slice of San Francisco life.
Walk around the Castro neighborhood for some cool shops, interesting people and iconic San Francisco landmarks (The Castro Theater marquee, for one)
Walk down the hill on 17th to Mission and Valencia for some great Latin-American food. Don't stray too far from the 16th-18th-Valencia-Mission-Guerrero area of The Mission District, as it does get dodgy on the fringes.