There have been a couple of threads lately about dry storage, ditch kits, etc.
Since I started paddling canoes 12 years ago I have used a plastic peanut butter jar to store my valuables. I can fit my watch, wallet, keys, knife, and cell phone in one of the big 40 oz. containers. For an extra measure of safety I atttached a small stainless steel eye-bolt thru the lid with fender washers inside and out. (sealed with silicone sealent) I use a lanyard to attach the jar to the boat. I have extras that we use for snacks, glasses jewelry and even the camera. They are handy at the beach as they keep your stuff in and sand out. They float and are pretty durable and fairly watertight (they seep a little if submerged for very long) Anything that I'm really worried about, I put in a zip-lock first.