We had a look at the Basin Moonwater waterproof backpack, which is a must-have if you want to carry your cell phone, camera or anything else that shouldn't get wet with you. It has suction cups that makes it easy to attach to the deck when you need to put it down to access it. A purge valve at the bottom of the bag allows you to squeeze out any trapped air in order to create a vacuum seal. You can even fill it with ice if you want the backpack to double up as a water-cooler.
Drycase also makes some great waterproof cases for phones and other electronics and offers a waterproof speaker that comes with different mounts.