It is necessary to keep your car keys dry when you are in the water and you can do this with a dry bag like the one above or you can get a tough key safe that will bolt onto the bottom of your car or any solid object and protect your key from theft by means of a number combination lock. Once the right combination is entered the door swings open revealing your dry and safe car keys.
The key Safe has the advantage of leaving you less encumbered which is better as, with all the gear that you will have on anyway, you will not appreciate a key flapping all over the place in a dry bag.
If you do go for the dry bag then best not to have it tied around your neck in case of entanglement with kite lines, you can stash down your wetsuit for more safety. The top portion opens vertically and is then clamped shut and locked down with a compression clamping system which forces the tough rubbery compound together.This works most of the time but very occasionally you will find that a small drip of water has leaked in or worse if you have ripped it or failed to shut it properly then your keys will be swimming.