The authorities are gradually getting stricter about wearing a flotation device while sailboarding and kitesurfing in Australia. In Victoria, the law states that you must wear at least an approved PFD type III device when windsurfing or kitesurfing unless you are with 400 m of the shore and wearing a 3mm wetsuit.
The problem with wearing such devices is that they are bulky, can obstruct your movement and access to you harness hook. I have however found a device that could overcome such problems.
The PFD I have found comes in the form of a bum bag. It has a CO2 cylinder inside and is inflated by pulling a yellow tab on the side of the bag. The device is approved by the US coast guard, and would possibly be approved in Australia.
I purchased the device from West Marine in the US. I got it shipped to Australia without the CO2 cartridge (since this is a shipping hazard, even though you sit atop one on every commercial air flight). I managed to purchase the exact cylinder (3/8" , 38 grams) from Whitworths in Melbourne.
Here are some pictures of the device. I inted to wear it as a bum bag to keep it out of the way while sailing. I am also trying to contact the marine board about Australian certification.