Personally I very much dislike riding with a backpack, even a light one, but have no problem with putting significant amounts of stuff in jersey pockets. So I surmise that the "fannypack" (they are bum-bags over here) idea has some merit, as the lower the weight is, the less one notices it. But really, what is the problem with simply strapping the backpack to the rack? It's not as if racks weigh much.