The thing I like about the Dacron line is it's diameter vs. strength. It is about the same diameter as standard dental floss, but it's strength is impressive. Seeing how well it works on landing lunker Sturgeon, I gotta think it is the best stuff for size vs. usefulness. It doesn't seem to rot nearly as easy as nylon does, either. Still, Mason line is good stuff too. If I had to choose between bulky paracord and Dacron line, I know which I'd rather pack.
Yep, lots of choices on type and size of drive.
As far as what to put on it, well, they may not be legal document copies as you say, but they can sure make getting replacements a lot easier. Everyone here keeps passport copies for just that reason. I think that is more significant than you may be alluding to, but certainly no reason not to keep the originals safely stowed as well, as you point out.
While it is not of much use in an emergency, it sure is handy to have medical/dental/legal records with you. From a survival standpoint, it might be a good idea to have your immunization record handy, although once again, a hard copy would be best.
Wills, treasure maps, etc. The list is endless. Of course, one little emp and the darned thing is useless again (oh no, I've started that debate again have I?).
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The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)