One of the beautiful things about touring (as apposed to backpacking) is that you can carry a lot of weight on your bike. So my question is, Why would you want to start carrying stuff on your back as well? I understand hydration pack if you think those are necessary in the area you ride (like desert perhaps) but to my way of thinking, why not just carry enough water bottles on your bike? It would be the same weight, down lower, and you can move more freely on your bike which translates to more comfort and longer riding.