We're the microbrew capital of the world. There's a ton of breweries, brew pubs, bars, and drunkards.
Public transit is not so hot in SD. It's passable, but not if you're in a hurry, or if you're trying to get to places that are outside of the main corridor (read: where the best breweries and music stores are located).
The Gaslamp district in downtown might be a good place to centralize around because there're a ton of shops, restaurants, and bars around it and it's condensed enough that walking is an easy option. The Yardhouse there has 100+ brews on tap.
If you're looking for more straightforward and familiar retail and restaurants, Mission/Fashion Valley areas will treat you right. You're near Gordon Biersch, Firehouse brewery and this weekend there's a craft beer festival going on there
Mission Valley Craft Beer Festival | thefullpint.com
If you're looking for a more beach party vibe Mission Beach, Pacific Beach, or Ocean Beach are good areas to check out. Pacific beach has the most headshops, bars, and tattoo/piercing parlors of the above.
. I am spending three days in San Diego and have Friday and Saturday to look around and see what there is to see (Sunday is spoken for). Will be in the Harborview area and I have to rely on public transportation to get around. Definitely hitting the Zoo, but other than that, what's close? A good brewpub would be awesome. 
