You definitely want to be prepared. Brings lots of towels, store the used and the dry in separate plastic bags, bring an umbrella, bring a change of clothes (and socks). The drier you keep your body the better off you'll be. Take your time drying off the discs and all that, don't rush.
I tend to throw less Champion/Z plastic stuff when it rains because it gets so slick. I try to stick with Star/ESP and base plastic.