Should I bring a change of clothes for Island's of Adventure?

I would not recommend wearing sweat pants. If you want to wear long pants, wear something like a light chino/khaki which will dry quicker. You can wear a poncho on the super-wet rides, but most ponchos do not cover your legs, only the top part. So you might want to go to a local store and see if you can find some kind of really long poncho. Or yes, bring a change of clothes. Juric Park usually gets you only a little wet (usually), but Dudley Do-Right and the Barges will get you SOAKED. So change out of your sweat pants into something else, go ride all of these rides, then change back to your sweatpants.