While I have not put one together yet...I was going with the Watertribe link when I do. All wrapped up in one package (maybe vacuum packed with LARGE tear strips). Vapor barrier to start heat retention, heat packs, gel shots, and probably a tea light with lighter or more probably easy to strike matches. All sized to fit in a cargo or life vest pocket.

In a dunking situation, getting the vapor barrier on is the largest step in recovery as it kills the evaporative cooling immediately. Heat packs are tear and use (i.e. immediate). Gel shots for carbs, and once you start functioning, a tea light between your legs (remember to vent your vapor barrier) for extra heat input.

All the insulation in the world only retains the little heat you are loosing. If you are dunked (cold water or not) it is far more efficient to use external heat to put heat back in your body, rather than rely on capturing your own heat.

Next step, add insulation on top of your vapor barrier.

Cavers routinely carry one or two lawn and leaf sized garbage bags in their helmet. Getting chilled, put one on, and in the old days, put your carbide lamp between your legs. Two layered works even better. Just remember to vent and be careful of the open flame.

Bill