Step 5: Buy!
Use the small plastic bags at each booth to gather your purchases from that booth and pay the vendor directly. Remember: cash. Then place your purchases in the bag you brought with you. There may be lines at some of the more popular booths, so be patient.
Most people who start shopping at their farmers markets just buy things like apple, apple cider, baked goods and maybe cucumbers. I personally started with eating a lot of carmel apples. Once you get comfortable with those really basic items, you'll probably want to move on to buying actual vegetables -- like tomatoes, greens, squash, peppers, etc -- as well as herbs, cheese and yogurt. The next stage is experimenting with vegetables you've never seen before, mushrooms and meats.
If you're going to buy meat, make sure you have a place to refrigerate it in your office. The market in San Francisco sells fish. I don't recommend buying fish if you plan on a long, crowded train or bus commute. Your fellow commuters will hate you. And for good reason.