We like water shoes just because the pathways and the bottom of the pool are rough. You can bring food and water if you want, but Disney prohibits glass containers of any kind. For our room keys and a small amount of cash, we found it was easier to buy one of those plastic containers that goes around your neck (about the size of a deck of cards). They're available in the main shop at Blizzard Beach and Typhoon Lagoon. Since it's not absolutely, completely waterproof, we also bring along sandwich or snack-sized ziplock bags to wrap money/room keys in first.
Cheers,