When are you going? Now (and through the spring) the water will be cold - just be prepared for that if you're planning swimming/surfing. La Jolla is a good choice to stay in, for access to beach areas (La Jolla Shores, La Jolla Cove, Windandsea Beach), and you can get to other beaches, like Mission Bay or Torrey Pines State Reserve. There are some good food options in La Jolla - lunch at George's Ocean Terrace, which has a great view; dinner at Whisknladle. If you like seafood, grab lunch at El Pescador Fish Market and have a picnic at La Jolla Cove.
Gaslamp is pretty touristy. For dinner I'd recommend the Little Italy area - Kettner Exchange, PrepKitchen (same company as Whisknladle), Juniper & Ivy are all good restaurant choices.
And you didn't mention transportation, but you will need a car. The La Jolla beaches aren't really within walking distance of each other, and there aren't great public transport options for getting to downtown/Little Italy/Torrey Pines, etc.
Enjoy your trip!