Thank goodness that you have me. I've picked out a few things that you should definitely bring along in your carry-on instead. (Because you really don't want to be one of those shivering tourists at SFO.)
A hat and a jacket: Why? It's windy and cold. You'll need layers to keep in the heat.
A scarf: By the way, it's really windy and cold.
Sunglasses: Even though it's chilly, the sun still comes out every once in a while. When it does, you'll be prepared.
Boots: I like these because they easily transition from day to night - and they'll keep your feet protected from the elements. Leave the flip flops at home. Even if you're blessed with a warm day, your bare feet really shouldn't be exposed to our streets.
Socks: Everyone is happier when their feet are warm.
An umbrella: Just in case. (Plus, this polka dotted one is so cute!)
(PS - I can't find the source for the top photo. If anyone knows what it is, let me know and I'll make sure the link gets updated. Thanks!)