how about an old style military backpack that come with the option of wearing as a backpack? i used something like this a bit in HS (wwi or wwi european canvas bag) which i bought in NYC at a random army surplus/"vintage" store. ...perhaps not as stylish or well-done as you were thinking, but it was certainly different and durable, but not always comfortable.
or look into streetwear brands (looks cool...on dudes), brooklyn industries, victorinox (comfortable and durable).
in the end, i like the idea of a satchel (like the example in the first response) if not a messenger.