Perhaps not totally relevent to a fixed wing ditching, but if you can attend a Helicopter Underwater Escape Training course (HUETS) it would help your survival prospects.
Learning how to get out of a sinking inverted bathtub without too much panic from yourself and crew and the sea survival techniques thereafter would be valuable.
I do not know where an individual can attend such a course in the UK (The oil industry presents them in-house) but there must be a school somewhere running a one day session. A few hundred pounds for a skill for life...