Anything and everything. I've been there many times that same time period. It has been warm, seasonal, cool, cold and frigid. Plan on packing layers. A little bit of everything, from shorts and short sleeve shirts to even coats, gloves and hats. Check a day or two before you leave home to get a trend. Not a forecast, but rather a trend for last minute packing. I have been there when it has been in the 80's and when it was in the upper 20's. Two different years Disney was covering up the plants and bushes to protect from frost.
Also, not sure where home is for you, but if it is cool/cold at all (Chicago here for me), remember you are usually not out in it a long time. You go from house to car, to shopping, to work, etc. At Disney, you are walking out in the open a lot, much of it near water. And standing outside in lines, etc. 50 might seem warm at home, but at night at WDW, it can be quite chilling. And in the 20's, downright brutal. Ask anyone who was there in early Dec, 2010.
Enjoy, a very pretty time of the year.