For an out of state visitor, Napa is better than Livermore, locals are more blase about the Napa experience. I would also recommend going to Sonoma, good wineries and nice old colonial Spanish town square. The key rec here is to go to wine country during a weekday, far less crowded than on weekends, especially in September. Weekends are good for doing activities or meals in SF proper or Berkeley, far less traffic.
Surfing in northern California is a bit of drag, the water being very cold. However it might be OK if there is a heat wave, which could easily happen in September. FYI Auburn fan, a "heat wave" in NorCal is when the temperature in coastal cities goes above 80F...
One fun ocean-going activity if you're into it, a bit more active than whale or shark watching, is salmon fishing out in the ocean. Usually in a small charter fishing vessel with about 7-10 other tourist/fishermen, all the material provided. You set out early at dawn and sail out in the Pacific for an hour or two in search for a salmon bank. I did it twice, and had beginner's luck, caught a 36lb monster, that the captain reeled in for me. Initially he thought it was a seal who got the bait, based on the strength of the pulling on the line.