You'll want to watch our weather reports as you get closer to your ETD. Typically the 60s is normal this time of year, but not this year (yet). It's been from 70s to 80s by the coast, 90 inland.
Jeans are a staple here in San Diego year round. For packing, you could get by with just a S25, but if you are going to do some shopping, then you may want that TS or BB for more room.
For EDC, probably just a SE.
San Diego has quite a few colleges and universities, so you do see some people with backpacks (more men than women). We do NOT have an extensive public transportation system. I do not feel safe on a bus as a woman alone, and the trolley I would only use for special events (like Comic-Con, Mardis-Gras, or a Charger game). Most San Diegans get around by personal car, not trolley or bus. So, maybe that's why we don't use backpacks as much as other cities, but you won't look out of place using one either.
Don't get me wrong....I love my city. There is lots to do here. But, we are a large city and we have the same issues as many other large cities.