Warmth:
Things that worked for me.
Two plastic bags one for each foot before you put your wetsuit on.
Your foot slides easily into the legs of a wetsuit.
If you sail with booties, leave the bag on, your foot will easily slide in/out of the booty.
For additional warmth wear polypropylene socks under the bag.
The foot is drier as the bag is sealed due to the pressure of the wetsuit against the leg.
Caution: there is less grip in the feet if you leave the bag on, I didn' find this to be a problem for my sailing style.
Safety:
Haven't tried it yet, will it work? Tie a rope around the rear footstrap (5 meters) and let it float/flow behind the board, when in big waves/wind. I would think that before the board floats away from you there is a chance to grab the rope.