Kayakbirder, We use deck bags for most overnight trips as a handy place for binoculars, camera, water bottle, snacks, sun screen etc. The bags we use have mesh pockets on the outside that we use for the water bottles.
While the deck bag has a "waterproof" zipper we always assume it will leak in a capsize, or if we capsize it could be at a time the zipper is not closed tight. We protect any non waterproof item with its own protection. Look at the way a bag connects to your boat and make sure it is compatible with your deck rigging and that the profile is not too high for your style of paddling.
Sea Kayaker Magazine