Spraydecks
For Kayak courses you need to bring a whitewater deck that fits onto your boat.
You want a deck that goes on easy and stays on until you want to open it again. It has to be tight otherwise it will pop off just when you don't want it to. But too tight is also not good as it takes lots of time and effort to put on. Peak UK and Playboater make great decks that are actually curved so that they sit better on the cockpit rim and go on easier.
Make sure that you size it to your kayak's cockpit correctly (as well as your waist size) as there are three sizes available: Riot, Keyhole and Bigdeck. Most important of all though is that you can get out of your boat if you need to in an emergency. Whether that's a wet exit or to portage or inspect a rapid. Corran Addison actually says that if you can't get your deck off without using your hands it's a death trap! If your stuck on a tree or rock and need both hands to support yourself then I can see his point there.
I can get out of my creek boat with my PeakUK deck without having to use my hands. Even though it only has a front release fitted I can use my knee to pop it off. However I actually think that deck implosions are something you should be more aware of on high volume rivers. They happen far more often than they should and can be just as dangerous on a hard high volume river than not being able to get your deck off without your hands. As such I do not paddle with a knee off strap on my deck.