1. Sunset Cliffs... obvious name, but some great sunsets
2. The farmers market is really fun to go to. Lots of great local food
3. OB & PB are fun just to walk down. LOTS of bars w/ local brews. OB is a little more surfer/skater vibe.
4. Little Italy is a fun area of downtown that has some neat stores / wine bars
5. Coronado is pretty cool - there are some beaches by Hotel Del Coronado that are really nice.
6. Mitch's Seafood is a great place to eat fish tacos by the harbor.
7. La Playa Taco shop in Pacific Beach... I donno why but I love this place - a little hole in the wall. You can rent Kayaks in Mission Bay which is close by.
8. Balboa Park --- if you do go to the zoo, have a walk through Balboa Park. It's gorgeous.
9. We stayed at an airbnb for really cheap... like 40/night. It was really nice and only a few blocks from the beach. It was like a mini apartment. 2 beds & a bathroom.
10. Have a fire at Mission Bay Beach. It can get a little cooler at night, so a beach fire is always nice. The best part of SD is just walking and discovering places. Ocean Beach, Pacific Beach, Little Italy are great places to start. Have fun!