One thing San Diegans love to do is fly kites! The steady ocean breeze and crisp blue sky make perfect kite flying weather. Just about every weekend in some park, or many parks, there are people flying kites. I was just walking around South Embarcadero park on my lunch break and found this guy (bottom left) sitting down and watching his kite fly.
There are several shops around town that sell all kinds of kites. In Sea Port Village, there's a shop called, Kite Flight- http://www.kiteflitesd.com/
Or, if you're closer to Point Loma and the airport, then check out Kite Country- http://www.kitecountry.com/
If you're here during the second Saturday of any month, you can join the San Diego kite club in Mission Bay Park from 11am to 2pm.