I've been thinking of mounting a rack over my rear tire, but wondering if it's going to be worthwhile. I have a small saddlebag which (barely) carries everything I normally tote: tube, breakfast bars, cell phone, wallet, house keys. Sometimes I think I'd be better served with a rack and a couple of bungee cords so that I could carry other stuff (even stuff I find out there). For instance, the other day I came across a book sale while riding, and bought three paperbacks, and kind of "juggled" them home.
But then again, how often would I use it -- and so therefore, is it worth it or not?