I have two messenger bags: the Triar, from Bally (~$1,000), and the Cornell from Manhattan Portage (~$70). The cheap cordura bag from Manhattan Portage is obviously much more casual than the calf-skin bag from Bally, but they share a few attributes. They both have:
a minimum of straps and closures exposed, yielding a clean look,
a convenient but barely visible side pocket to slide a newspaper or boarding ticket into,
roughly the same ~11-liter...