I would get an aluminium case or some other metal, to transport the Kindle in, in a rucksack. I don't really think leather or other cases are sufficient to withstand the kind of forces your Kindle is subjected to when carrying it in a rucksack with a lot of books. Some say that it can be done, or they have done it with just a sturdy cover. In my opinion they've been lucky till sofar. I mean: I've seen my teenager throw her rucksack with expensive calculators and such in it around;you would't believe it. Or schoolmates that did it for her.
Or you could transport your Kindle, with a sturdy cover in a seperate bag, like Kindleworm says.
