I certainly wouldn't want to second-guess the pilot in question, especially without knowing more details about what happened. But I don't think ruminating about a hypothetical situation is a bad idea. Armchair QB'ing can be odious if it descends to the level of "That guy was a moron, I would have done this and this and that..." but as Peter Garrison pointed out in Flying magazine, the time to start thinking about thunderstorm avoidance is not when the sky is black and purple and your hands are full of airplane, it's when you're sipping hot chocolate in your air-conditioned living room, reading about some other poor b***d who flew into a thunderstorm.

Realistically, I think scrambling out of a submerged, inverted float plane in the Arctic, in winter, with the temperature close to or below freezing, is pretty much the worst-case scenario for survival, and kudos to this pilot for handling it as well as he did. Any electronic equipment (such as a cell-phone, handheld radio, or GPS) is likely to be waterlogged junk; any bulky survival equipment is at the bottom of the lake or river. Anything that's not in your pockets or around your neck can't be relied on.

I think there's going to be an unfortunate trade-off in this situation - you don't want to be wearing a bulky overcoat when the plane goes in the water, much less a backpack; so likely - assuming you get out of the plane and make it to shore - you won't have a lot of equipment. Being able to build a shelter and a fire quickly would probably be imperative. (If there's a known shelter nearby, as there was in this case, it makes sense to head towards it, but at those temperatures, even a walk of a mile through heavy snow and/or woods might be too much for someone who's lightly dressed, wet, and hypothermic. Maybe a couple of energy bars would help to stave off hypothermia, so I'd probably stuff a couple of those in an inside pocket.

Basically, what I'd want to have (and what I think I might realistically fit in my pockets):

SAS Survival Guide
Altoids PSK
Esbit Stove (or at least a couple of fuel tabs) to start a quick fire)
Space Blanket
Redundant means of starting a fire - mag-flint, Bic lighter, waterproof matches, WW2 flame-thrower ... <img src="images/graemlins/wink.gif" alt="" />
Good quality knife to shave wood for kindling (feather-sticks)
Waterproof tinder (a small bottle of Purell Hand Sanitiser).
Handful of energy bars
Cord for erecting a windbreak or shelter
Wool clothing
Waterproof flashlight?