I think Richie has a Kindle with him on Richie's World Tour or Go Mad on a Nomad -- see
http://www.thorncycles.co.uk/forums/index.php?topic=4851.0 -- for how he uses it.
I have an iPad, an iPhone, an Android smartphone, and none of them will have battery power left after more than a day's local ride if you use the GPS even sparingly. As touring companions they are simply a nuisance.
Unless you want to go into contortions with solar charging or hub dynamo charging, none of which works either well or at all, or for more than one pretty small device, the only tablet worth considering is the plain Kindle, and that only for it's outstanding battery life and it's excellent screen for plain reading. On every other aspect (maps, sending email) it is slow, though Richie and others claim the exceptional battery life makes up for it. The battery does last forever, and I suppose that's what matters most when you go bush. After a three day credit card tour with a good deal of map reading and book reading deep into the night, and a thrice daily visit to the groups I correspond on, and e-mails home, I put the Kindle straight back on the bookshelf because it didn't need charging. (I just took it off the shelf to describe it accurately, and it turns out to have some charge left after a year or so on standby... Try that with an iPhone...)
However, the Kindle has another advantage not mentioned above: over at least part of your tour it will give you a free connection to the internet. I don't know if you still get that with a new Kindle but mine has it.
PS I have a Kindle 3 keyboard model, virtually new (I'm a writer, I bought it for professional purposes for which it is too slow, and replaced it almost instantly with an iPad), for sale, complete with expensive, thick, wrinklefree, glare-free screen protector and expensive Tuff-Luv leather (maybe PU -- it's suspiciously unmarked even considering it got so little use) case with built-in stand, charger, cable, all packaging, instructions, free connection to the Internet. Drop me a note at andrejute at coolmainpress dot com if you're interested. I'm in Ireland and the charger is for European voltages. Comes with a set of CoolMain Press ebooks by me and some authors I edit.