I'm no longer a fan of backpacks as "daybags" and would much prefer a messenger/shoulder type bag.
While I know there is a Packing Cube Shoulder Bag, it looks too much like a purse and as a member of the male persuasion, it's just not going to cut it.
But what about making a Packing Cube Messenger/shoulder bag the same size as the ones for Aeronaut and Tristar/Western Flyer currently in backpack style? All that would be needed is to add a couple of "D" rings instead of backpack straps. No strap needed as the strap used for the larger bag (Aeronaut, Tristar, WF) could be removed and used with the packing cube bag. (And don't forget those "o" rings inside.)
Does this make sense?