Lyee C.
Yelp
District Market is the convenience store to hit in SFO for those "ah, I forgot to pack something!" moments in Terminal 3.
Yes, it has food, beverages and snacks for purchase. But you can find those elsewhere. District Market is great in all the other things it also has. Books, chargers, headphones, things to amuse your children on the flight, clothes (not just the souvenir ones), luggage, bags, travel toiletries, a small cosmetics section and even some wine.
And, the stars for me: See's Candies and Ghirardelli chocolates. The two local specialty gifts I bring to people when I fly out of SFO. I tend to forget to grab gifts, or maybe another person is added to my itinerary at the last minute. District Market has saved me many times regarding last minute gifts.
The store is located right by the main food court in the terminal, and next to the restrooms. Self checkout kiosks galore in the store. Like most airport stores, it's very lightly staffed but easy enough to find what you need by the clearly marked sections of the store.