Apple's aluminum wireless keyboard works without problems. (I have the small one.) But if you're backpacking you'll likely be getting a sturdy cover for the iPad anyway, so you might want to get one of the combination cover/keyboards, simply for the compactness of the two together. There's a bunch of them on this Gadget Review page... http://www.gadgetreview.com/2012/11/11-of-the-best-ipad-mini-keyboards-list.html
Be sure to read the comments at the bottom of the article! I found out there that some of the keyboards mentioned don't even have a Command key -- meaning they're designed for other tablets, not the iPad. I suppose the giveaway is the Photoshopped in pics of the iPad with the icons pointing sideways. LOL!