Ponchos are an excellent way to stay dry on water rides. They are lightweight, reusable, and can be folded small enough to fit in small spaces like in backpacks or purses.
For your feet, shoe covers can save your socks and sneakers. They are typically made of disposable plastic or silicone and can be worn with almost any shoe.
Instead of bringing your own poncho, trash bags and plastic bags from any retail establishment will work. Add extra protection by using duct tape to secure the bag to your ankles.