There are alot of things to do in San Diego. For fishing you can go out on the party boats from Mission Bay. Should be pretty cheap $20 or $30 bucks I would guess. Seabass, Tuna, Bonito, Halibut, and the like.
You can also find out what days of the week some of the local lakes are open for fishing and can usually rent a small boat. Lake Moreno is about an hour east of SD on I-8 and used to kick out alot of 1 to 2+ lb bluegills from shore when I lived there.
There is also Seaworld, Balboa Park, San Diego Zoo (one of the worlds best), La Jolla Cove (snorkeling), Blacks Beach (nude), boardwalk from Ocean Beach to Pacific Beach (rent bikes or skates and cruise for great people watching), Killer Mexican food and not that Tex/Mex or MN bean filled cr*p, Tijuana (walk across the border rather than drive), Old Town, Lion Country Safari, Mt. Laguna, Mt Palomar observatory, and oh so much more.
Have a great time.
The great thing about San Diego is that the weather will be perfect every day that you are there. No bugs and no humidity.