One of my favorite places in San Francisco, hands down, is the Ferry Building Farmer's Market. Its an excellent example of California farmer's and excellent food, coffee, sweets and other goodies. They even have an independent bookstore. My favorite food location is Primavera, its a delectable take on fresh Mexican food and Boulette's larder with the best selection of every spice you'd ever need. Blue Bottle goes with out saying as the best coffee in the place but you'll have to wait in line. Its worth it. The cappuccino is unbeatable and their standards on buying etc are uncompromising.
Wandering this area is the best way to enjoy a Saturday morning.