Layer your clothes - sweatshirts, definitely -- we're expecting rain this Saturday/Sunday (it should let up by Sunday), so bring a poncho, unless you want to spend the $5-$6 for a Disneyland poncho ...
It gets chilly at night, so you may want to bring a jacket - you can get a locker for all day - but they're running $4 these days - I would recommend a backpack and stuff your jacket in there to save $