I used to use a backpack, but got sick of the sweaty back and having to bring it everyday.

I finally bought a rack and panniers for my IRO Rob Roy and now I load it up with clothes, food, etc once a week and heft it in. Other days I just ride my road bike with nothing but the clothes I'm wearin', a cell phone, and a basic tire repair kit. Having nothing to carry on most days is the best and allows me to do a lot of extra "training" miles.