Paddle float
From KayakWiki
These devices are used to perform the paddle float self rescue. They can also be used in an emergency to fill a dry storage compartment that has flooded and needs extra buoyancy, to provide extra stability to a paddler in difficulty or other uses. Some paddlers will use them as an aid when wearing a dive mask and snorkel - you can drop to the surface of the water and look under without completely overturning.
The typical paddle float has 2 inflatable air chambers separated by a sleeve that you slide your paddle into. They have a lot of flotation but require a bit more time to secure and inflate. They typically cost $35.
A rigid foam paddle float is also available; it doesn't require inflation. You slide your paddle into a sleeve and secure with a strap or buckle and off you go. They are much quicker to secure and use but are bulky to store and don't have as much flotation. They typically cost $45.
If you are a light paddler, a foam paddle float is useful. Heavier paddlers will need an inflatable paddle float, as the foam one simply lacks sufficient buoyancy.
Another option for the "do it yourselfer" is to make your own out of closed cell foam and a bag or duct tape.
The most important thing, regardless of which option you choose is to go out and PRACTICE WITH IT!!!! Reading instructions in a book or on the Internet are no substitute for real experience and practice. Your technique will suck the first time you try it. Would you rather your poor-technique first try was in a safe, controlled practice situation, or in a real emergency?

