Unfortunately, there is no substitute for hard copies. Depending on electronic media is also depending on power to operate the equipment needed to read it. :)
I was thinking more along the lines of a BOB or I'm Not Coming Home (INCH?) bag use. A solar recharger would hopefully work, if they use standard batteries like I -think- other PDAs use.
------They may look intimidating, that's by design; but they aren't bulletproof. -------