One of everything - this is my favorite time of the year to go, but the weather is TOTALLY unpredictable. It can be in the 80s or in the 30s (in the same week).
I go prepared to layer. Unless it gets really hot I can be okay in a short sleeve top and long pants, so I usually just take one pair of shorts. Longsleeve shirts make a nice light jacket that can be removed easily when in the sun.
I take a lightweight velour jacket - if it gets really cold I'll put on a longsleeve tshirt, corduory or flannel shirt or maybe a sweatshirt and the jacket.
Buy those really cheap $1 gloves before you go. Having your hands warm can help a lot. I also pack a long scarf that I can use to cover my head if the wind is blowing a lot. The humidity can make colder temperatures worst than you would think.
Most of the time it will be in the 70s during the day and 50s at night, but you have to be prepared for the other extremes as it is not totally out of the ordinary to have temperature swings.
