When I go to WDW (or anywhere that has AC), I always bring a light sweater or a lightweight summer scarf, because my arms can get chilly. I especially like the scarf, because it works as an accessory to tie an outfit together, and if it gets too hot, where it's uncomfortable around my neck, I can just tie it on my purse. It weighs less than a sweater. It's just enough to keep the chill off my arms, and breeze off my neck, if I need it. I'm actually hot most of the time, but air conditioning can get to me.