As I'm coming from New England the day after Thanksgiving, I'm wearing a pair of jeans, polo shirt and a fleece coat (as it will be quite chilly up here), and am packing shorts, short sleeved shirts, bathing suit, several pairs of new socks, pj's, and a couple pairs of yoga pants. I never under estimate what the weather will be. Went one year and they had a cold snap. Even for us from NE, it was cold. Saw a family at the TTC one morning freezing, as all they packed was t-shirts and shorts. As soon as they got in to the Magic Kingdom, they made a beeline to the Emporium. The following year it was cool in the morning & evening, but nice during the afternoon.
I recommend bringing a sweatshirt (or fleece jacket/pullover) and a pair of pants. The evenings can get cool. Better safe than sorry.