I rented a car to visit the Muir forest, a 30 minute drive from San Francisco where you can see redwoods. It's a bit crowded, but the walk is family- and even handicapped-friendly. If you're up for a longer hike, there are tougher trails and you can easily spend a hard day hiking there (or just a 30 minute walk on the boardwalks).

Otherwise, I stuck with taxis. SF has a pretty good public transportation system based mostly on buses and the occasional cable car, but they're slow. Unless you want to spend 45 minutes getting across town, just grab one of the plentiful cabs. The shops in Chinatown are worth seeing, though you won't feel immersed in the Chinese culture like you will in Chinatown in NYC (for better or worse). For hippie- drug-themed shops (head shops), check out Haight-Ashbury, which is near the Golden Gate Park. Visit Castro Street to see the famous theater and to immerse yourself in the gay culture.

Don't bother visiting Seal Rock. Instead, spend your time at the Golden Gate Park, which is about 4 miles long. You can easily spend an entire day exploring it (if you have the energy). While you're there, the Japanese Tea Garden is nice, but you have to pay to get in. The AIDS memorial garden is almost as nice, and it's free. The San Francisco zoo is one of my favorite zoos in the country, because the environments are nice and the views aren't blocked by fences.