Go for a walk or bike ride and enjoy some time outside.
It is homecoming weekend so avoid campus on Saturday - traffic will be very bad. But, if you are sticking around after the weekend check out UC Berkeley - walk around campus, wave to Deborah's office at the law school, and take the elevator to the top of the Campanile for a beautiful view of the Bay.
You won't have much time on Saturday, but if you are in town long enough. . .the Ferry Building in San Francisco is beloved by locals and tourists. A fun foodie destination with amazing views. You can take the BART or the ferry across the Bay!
A nice place to walk around, grab a cup of coffee, and/or go shopping.