I hate the sweaty back, too. I also hate riding with anything on my person. Alas, I finally realized I had no other option but to bite the bullet and invest in a HUGE backpack made for cycling in which I could stuff EVERYTHING in while keeping it waterproof. Work shoes, extra set of clothes, food, computer, some tools, toiletries, U-lock, hand pump and inner tube, keys, EVERYTHING fits nicely and safely in my Chrome Ivan bag. A little hipster? Yes. Made my commute much much much easier? Yes. Affect my balance and ride? Minimally relative to a North Face bag or one-strap bag (yes, it still is a backpack like any other, but I find that I can adjust it to a place on my back for optimal balance). Sweaty back? Of course, but there's plenty of room for an extra shirt in there, and the bag itself has a backing material that dries extra quickly.