FWIW: I flew for US Customs in the Caribbean and with the Civil Air Patrol on over water patrols for many years. I often fly over water in my airplane having done many trips to the Caribbean, Key West, Cozumel and Cancun. I recommend taking some kind of water survival training (dunker) if you can. With Customs I took mandatory survival training every year. They concentrated on water survival so I have a good idea of what to expect. There were a few things I learned about water survival that opened my eyes.
The 1st thing is that if you have to ditch, you will probably want to get out of the airplane as soon as possible. That means that if the survival gear isn’t strapped to your body you probably won’t have it when you leave the airplane. I know I will not go back into a possibly sinking airplane to remove anything once I am out. So if the airplane sinks, that mandatory expensive ELT installed in the airplane will go down with it and the signal will not be picked up by anybody. That is why I have my survival gear, to include a
personal ELT with GPS capability and a Marine VHF Radio strapped to my life vest. You want to minimize the amount of time it takes rescuers to find you, hopefully within 24hrs. Remember, if it is strapped to your body it is survival gear. Everything else is camping gear.
Another thing is that it is extremely difficult to climb into a life raft in open waters. If you do not continuously practice this, you will probably run out of energy trying to get in and not be able to stay afloat. If you don’t believe me, try getting into a small raft in the deep end of a swimming pool. It will open your eyes on how hard it really is. Now add wind, waves, adrenaline and possibly an injury and you will see what I mean. This is why I don't carry a raft. I don't say to not carry a raft in the airplane, but you are much better off wearing a good life vest than carrying a raft in the airplane. In my opinion those "around the waist" airline type life vests with a life raft only provide a false sense of security.
I personally wear
a high quality life vest whenever I will be a significant distance from land with a
GPS-PLB and a
Marine VHF Radio strapped to it from the time I get in to the airplane until I have landed and shut the engine down. Again, you want to minimize the amount of time it takes rescuers to find you. If I am flying over the warm waters of the Caribbean I am not very concerned with hypothermia setting in quickly, but not the same if overflying the North Atlantic.
Finally, no matter how shallow the water is, if you can't stand up with your head out of the water you might as well be in 1,000 feet of water. Don't get lulled in to a false sense of security just because the water isn't very deep.
Just my 2 cents.