If you happen to be in San Francisco on a Sunday during the summer I recommend going to Stern Grove Festival. Sure, it's a trek from downtown SF but it's worth it. Every Sunday Stern Grove has free concerts and performances in their park. I went with some friends last Sunday and we had a picnic and watched the SF Ballet. First of all, how do they move that way? And secondly, I love picnics in the park. We had olive bread, cheese, tomatoes, avocado, chips, salad, gummy bears, fruit and cookies. What more could you want? Pictures were not allowed, so I didn't get to take any (shhhhh okay, I will be honest, many) but I did capture a picture of the beautiful tomatoes we consumed and some of the ballerinas performing. Stunning.
If you do go, get their early so you can get good seats. Otherwise, be prepared to sit far away.