Afternoon Tourist walk
A great way to see a lot is to take a water front tourist walk from Pier 39 to Ghirardelli square. Start at Pier 39 which is the closest thing San Francisco has to DisneyLand. Lots of shops and restaurants. I recommend Trish's mini doughnuts, and the Chowders for clam chowder. Once you leave Pier 39 turn right and continue West along the waterfront. This takes you right into Fishermans Wharf where there are tons more things to see. There are lots of places to get fresh seafood, and if you have time Scomas is the best place to get crab, but it's very busy and priced accordingly. Boudin's makes amazing sourdough bread creations, and their sourdough bread bowl is fantastic. If you order one downstairs at their cafe it is half the price as eating the same one upstairs in their restaurant. Walking through the wharf there are more restaurants, and as you get to the end you should see Ghirardelli square up on a hill. Venture in and past the south-eastern most place where there is a line of people waiting to order sundaes. There is a second store in the middle of the square that sells the same stuff, and is almost always less crowded. If you still have time head South to the Buena Vista cafe, where Irish Coffee was invented. There is a cable car route that starts across the street from Buena Vista and if riding one is important you can hop on there.
Afternoon shopping and dinner
Take a Lyft to the intersection of Union Street and Octavia Street. This is the start of a long row of street level retail stores. Call the folks at A16 and ask for a reservation over an hour from the current time. Whenever their next available time is, that's how long you have to stroll. It's one mile if you want to hustle. (Backup restaurant is Mamacitas). Head west down Union Street and stop where you are interested. For women’s clothes, Ambiance should be on your list. For a Yoga class, Aha Yoga. For drinks the Whiskey Bar in the back of Marengo, the Blue Light for a local dive bar beer, and the West Coast Wine-Cheese Company for a glass of wine. Once you hit Fillmore Street turn right and head North. Rapha Cycle Club and Roma have strong espresso and The Balboa Cafe has bartenders dressed in pharmacists outfits from the 30's. Continue North, crossing Lombard Street and turn left heading West on Chestnut Street. Chestnut has more fun shops and an Apple Store. Lucca Delicatessen has fantastic sandwiches, and Tacolicious serves filet minion tacos and Micheladas. Towards the end of the retail section of Chestnut are the restaurants Mamacitas and A16.
Full Day bike ride
Ride a bike across the Golden Gate Bridge to Sausalito and then take the Ferry back. Best place to rent a bike for this is Sports Basement in the Presidio. If you don't take a Lyft to Sports Basement, you can leave your car in their parking lot all day. For a carbon fiber road bike you have to reserve one ahead of time, but for a standard hybrid bike, you can pick one up day-of. If it's 70 F or above and a weekend, get there early as they will likely sell out. Once you have your bike take off towards the Bridge, which you should be able to see. There are signs that guide you to the GGB, or just follow the dozen other folks you see that are probably doing the same thing. Once you cross over the bridge follow the signs to Alexander Avenue, which descends right into Sausalito. Go about half a mile past all the people and shops and look for bike parking near where the Ferry departs. That's your ride home so check their schedule. Once you know which Ferry you want, keep walking down the road. A fun spot is Bar Bocce, outside the main drag, but right on the water. There is a fire pit outside, and a Bocce ball court. You can eat in the restaurant or they will deliver food to the beach. If you have a blanket handy you can eat on the beach. If it is a nice day out, return to the ferry early, as a lot of folks will be riding it. There is a separate line for people who have bikes. Once the Ferry arrives in San Francisco, it is a fairly flat ride back to the Sports Basement. If you stick to the coast, the only hills is Fort Mason park. As you descend from the top of the hill you will pass by a large grassy area. This is a fun spot to stop for a while and take in the views. As you continue West back to the Sports Basement you will pass Marina Beach. It's another great spot to stop and enjoy the views.