Personally, I hate carrying a backpack too. But there are occasions when the mule (myself) must shut up and put up. So I bought myself what I consider the BEST biking backpack ever. I got it from an online store called Altrec. I bought a Deuter backpack. It has this nifty little thing that's kind of like a trampoline that is mesh and keeps the pack suspended up off of your back. No more super sweaty back and no more of those shoes or whatever else digging into your back while you're pedaling.
I have seen them for sale from Title 9 too but I found it cheaper at Altrec. Look into them, I wouldn't give my pack up for the world.