Actually, I'm not sure how fancy you really have to get. I've seen several accident reports where the plane was well and truly hammered (and toasted) and the NTSB was able to access memory in ordinary components.
I'd wrap the thing in fiberfax and stuff it in a steel box. Electrically, I'd have a USB jack outside and a USB socket thermaly isolated from the shell inside. Connect the data/power lines with teeny tiny wires (hopefully, they'll melt before transmitting too much heat to the thumb drive).
Next problem... :-)
Ron Wanttaja