Day One:
Walk downtown. Ride the cable cars. Eat lunch in North Beach. Irish Coffee at the Buena Vista at 4p after the fog rolls in. (make everyone bring a jacket so you don't have to buy the $75 fleeces at Fisherman's Wharf). Eat a late dinner in Chinatown. Can't beat the House of Nanking.
Day Two:
Rent a car and drive up to Marin. Breakfast in Sausalito. Fred's, Lighthouse, Bayside - take your pick. Drive up to Muir Woods for the redwoods. Feel free to get off the main trail. Picnic lunch at Stinson Beach. ( No need for a bathing suit. Too cold to swim.) I'd recommend visiting Tiburon for dinner, but Guymas is closed and I don't know what's moved in. Mill Valley will have good choices, and I always liked the Buckeye Roadhouse. The Mountain Home Inn on Mt Tamalpais would be a homerun, but can be tough to get into.
Day Three:
By now you're going to be tapped. Sleep late. Have brunch at Delancey Street. Wander down and buy tickets to the Giants game. They stink this year so tickets will be cheap. Enjoy the view of Oakland and the surprisingly good craft beer at the park. Food is good too. Walk back to the hotel and eat anywhere that looks interesting. I guarantee it'll be terrific.
Remember that SF is both hot and cold in September. It'll be 80 at 11am and 55 at 4pm, so wear a shorts and a bring a jacket. Leave your MAGA hat at home.
Great. Now I'm homesick.