You can drive accross the bridge amd do lunch at the Hotel Del (Coronado) and walk around town.
You can head to Balboa park and do any one of the phenomenal museums or walk the Botanical Gardens.
You can jump on the train and go down to the Gaslamp for lunch, or to Old Town for lunch, maybe check out the Whaley House (haunted, alegedly).
Or maybe the Presidio.
You can do the Midway tour amd the previous poster is correct about the fish tacos.
You can tour the Star of India, three mast tall ship.
You can head to Little Italy for lunch. The Waterfront Bar is one the oldest in San Diego and while no longer on the water, ised to be. Great burgers, too.
You can head to Ocean Beach and get the actual best fish tacos in San Diego, where locals go, South Beach Bar and Grille or to Hodads for an as seen on Diners Drive Ins and Dives, burger.
So much to do in the Sandy Eggo. So much.