yeah def do the zoo, where are you staying?
u can drive down to mexico and see it just dont go over, there is a really legit outlet mall down there. it takes like maybe 15mins form the city to get to the border, but not worth going over right now, my mexican friends dont even go to TJ its so bad.
pacific beach is a good time, lots of bars on garnet, if you want some good sushi theres this place called MIKA sushi, on garnet, i HIGHLY recommend it and the tavern at the beach is prob my fav bar there
gaslamp downtown is def a good idea, lots of places to eat, clubs and what not.
tons of malls to go to, id check out fashion valley tho, one of the best IMO.
la jolla cove to see the seals and you can hit mount soledad, this can be done in a morning, def not a full day thing
there are tide pools at the end of point loma you can go to, pretty cool and you can get some good views of the city from out there.
renting a boat or jetskis in mission bay is fun. as well as renting beach cruisers and cruising around the beach areas. and although the water will be cold renting a wetsuit and surfboard is def fun.
julian is this older town up in the mountains, they have great homemade pie up there, thats thing to do i guess, drive up there to get pie. haha never done it but yeah, its a cool drive out there, and you can go a little bit further and check out the desert, you can get atvs/dirt bikes too.
mission trails park is a cool place to go hike, pretty close to the city and it doesnt take tooo long to climb cowels mtn, great views from the top
but yeah just pm me if you wana meet up or just know more about something, SD is great, youll love it