An eReader can be an invaluable survival or teaching tool.
You are talking about a device that can hold the equivalent of upwards around 2000 books (and that's just in the main memory)
Mine is loaded with around 20 survival, edible plant, poisonous plants, mushroom collecting, etc, books.
with a bit of care they can be made extremely stable to transport.:
For mine I purchases a Patagonia case and lined it with close density foam. Before it goes in my bag it is wrapped it a water tight bag.
I've heard the argument about battery life:
Well some of the black and white models have a battery life of up to two weeks, and with the purchase of a cheap solar charger that quickly becomes indefinite. They can be found as cheaply as six dollars, though I would invest i something a bit better myself.
Most will read any form of PDF file so there are literally millions of books at your disposal and any book from your own library which you scan into PDF format.
Let your imagination run wild. You can even find guides tailored to your specific area.
Just remember that the full color versions, though nice to look at, do not have nearly the battery life. we're talking hours compared to weeks.
FYI: for Cellphones such as android or Iphones you can also download either the NOOK or the Kindle software right from their web sights, though again you run into the situation of battery life.