REI has the Flash 18 and the "Stuff Travel Pack" for about 30 bucks. For years I have used a Lowe Alpine Attack Summit (how's that for a hairy chested, macho name?) in a variety of ways, including carry on when flying and as a stuff sack that converts to a day pack for side trips when backpacking. A pack of this type is really versatile and handy in many ways.

One might be dubious about the comfort of the mesh straps featured by most packs of this type, but they are surprisingly comfortable, even when slightly overloaded.