It depends on your rides. If its a long ride, an all day thing with no convenience stores along the way, then you need to carry your provisions. But if you can manage otherwise, there is no need for a backpack.

As an alternative, I use Mountainsmith Nitro. This product is a fanny pack. So your back stays cool and I can carry stuff and eliminate the need for a saddle bag.

http://www.buy.com/prod/mountainsmit...208158905.html