SF essentials: leather knee high boots, a scarf (one should always be in your bag because SF is generally very windy), a cardigan of some sort, and a jacket that can break the wind chill. It's rain season now in SF, so you might want to bring an umbrella. In the 6 years I've lived in SF, I've never worn a hat, but you might want one if you're going to brave the boat tours on the water near the wharf or walk on golden gate bridge (which is probably freezing this time of the year with all that wind! So bundle up!).
LA essentials: a light jacket for the cold nights. LA is still the desert, so that means warm days but colder nights (around a 10 degree difference if not more). I wouldn't recommend wearing flip flops this time of the year in LA even though it's been 80 the past few days, just because that's not the normal temperature this time of the year. But, you might want to bring a pair just in case it does stay that warm.
I personally can't wait to go back home to SF...New York is FREEZING!!