You likely won't ever need a heavy winter coat, either, but even in summer, you're going to want a light jacket in your suitcase.
A crewneck sweatshirt, in addition to the light jacket, is my next San Francisco outfit essential. You can easily throw it over your shoulders if the day warms up.
Along with that light jacket/blazer, you're likely going to want to dress things up with a chunky (but not woodsy)
scarf in fall or winter!
It's not Boston, so you don't want too many warm sweaters
(if you've brought your jacket and sweatshirt), but a few tops and light sweaters should do just fine.
Even when baseball caps aren't trending nationwide, they're a classic in SF. Leave the logos at home.
As with many destinations,
purse-wise, you can't be a basic Longchamp in my book. Foldable, squish-able, getting wet-able, & cute - the perfect combination!