Dry Storage on a Boat

Nah, just use regular zip-lock bags and leave some air in it, so that they float. Don't use vacuum sealing unless you want to dive for them.

Digital cameras should be in ziplock bags too. If a few drops of water get into the bag, that's OK, just don't immerse the camera in water. Duck-tape a lanyard or headband to the outside of the camera bag, so that you can hang it or tie it to a railing.
Spare camera chips should be in old film canisters and in the camera baggie.

Disposable cameras are waterproof and float. They can be dropped into the water dozens of times on canoe and kayak trips.