I rack my backpack, but I do it a certain way. I run a bungie from the seatpost to the back of the bikerack, and slip the backpack in there. It's quick and fast. I use a backpack with grommets on the side and put D-Clips in there to make certain the back pack stays in place. When it rains I put a kitchen trash bag over the back pack and don't use the clips, which is what I did for 15 years before adding them. Even without the clips, I never had a backpack fall off, even when the bike tipped or fell.