They are listed in no particular order:
Take a picnic at an Off The Grid food truck site. Make sure to save room for food truck dessert too.
Spend the day (or part of the day) at Chrissy Fields Beach. The beach is in the northern part of San Francisco. You can see the Golden Gate Bridge from the beach, but you don't have to deal with all the tourists. (Win!)
Thrift store shopping on Haight Street in San Francisco. The street is packed with awesome thrift, vintage, and antique stores. Heaven!
Take a trip down Coastal Highway One. Enjoy the scenery, stop at abandoned beaches, grab food at cute roadside cafes and restaurants.
Enjoy an ice-cream cone from Birite Creamery (basil and lavender are my favorite flavors) while strolling through Dolores Park in the Mission District of San Francisco.
Drive up to Twin Peaks and take in the view of San Francisco. Make sure to admire all the cool architecture of houses built into the side of the hill on your way up (or down).
Head north of San Francisco to Bolinas Bay to watch surfers and explore the cute town. Or...rent a wetsuit and board and try it yourself. (There is a gentle surf in Bolinas so it is good for beginners.)
Get dinner at Pacific Cafe, an older seafood restaurant on the edge of San Francisco that gives you free wine while you wait for a table. (Their salmon and shrimp dishes are amazing!)
Grab some quarters and enjoy the old penny arcade on Fishermans Warf in San Francisco. Such an interesting place filled with old games brought back to life.
Make a fire on Ocean Beach or Muir Beach (only beaches that allow fires).
Couldn't forget this one. Explore Sonoma wine country (less touristy than Napa). The best way to do it is to rent bicycles and ride to the vineyards.