I have this women’s backpack from Deuter. This is a great travel backpack because it is just the right size to carry on planes. The size I have (32L) is relatively small but large enough to carry what you need and not so large that it weighs you down. There are many pockets with access from different point, and the padded shoulder straps and waist straps make it easy to carry.
However, one of the best design features is the mesh panel at the back which separates the pack from your back. It is incredibly good at keeping the user cool while carrying the backpack in hot weather. The only downside of this is that it is somewhat rigid, so it’s difficult to bend the panel if you need the pack to fit in a tight area.