My 2 favorite paddlers and I often use CO2 cartridge manual inflatable pfds, which we put on before we get in a boat--that beats a passive PFD not worn because it's too warm out. I have never seen a video of someone successfully donning a PFD in rough water and doubt it can be done easily unless one is in shallow rough water, maybe knee deep. West Marine sells inflatables in several varieties, including manual (you decide when to inflate) and automatic (inflates when wet, not sure if that means submerged or splashed) The inflatables at West Marine do not, however have flotation on your back, AFAIK, so your head will stay out of the water, but your torso may not. flotation 26lbs or 35lbs .

FWIW, I also have an Astral that is vented and cooler than most PFDs for kayaking. a link:
http://www.nrsweb.com/shop/product.asp?pfid=42103 flotation: 15.5lbs