There are quite a few good places to eat in Gas Lamp. I really enjoy Cafe 222 for their breakfast. La Jolla has some damn good food too (Cody's...also breakfast type food is amazing). Old Town isn't bad for Mexican.
USS Midway is pretty cool if you've never been on a decommissioned ship, although if you have I might skip it.
Sea Lions at La Jolla is a fun way to kill a few hours.
Balboa park has a good collection of small museums, and if you want to go to the zoo it's right there. I've still never been, but apparently the Safari Park is even better; but it's like an hour north.
Cabrillo National Monument is pretty cool. Consists of a lighthouse and views of the bay, ocean, North Island, and you can see into Mexico.
Hotel del Coronado is a fucking cool ass old hotel.
That's about all I can think of off the top of my head. The best thing is just go there and enjoy the absolutely amazing weather as much as you can. Since it's spring that's not as exciting, but just keep in mind that it's the same temp year round.