I always use backpacks when I travel. I just so convenient.
When I got a pack for my round the world trip (which never happened, unfortunately) I was around in every store in northern Ca. The only one that fit my back (I have a curvy back) and was comfortable loaded was Dana Design's backpacks.
When ever you decide how much stuff you're going to bring and find a good size pack that will fit it, go one size smaller and toss out some stuff. You will end up not using half and you will save your feet and back.
Also make sure get GOOD shoes with soles that are made for your feet.
http://www.danadesign.com/packs/
Good luck man
