This idea was shamelessly stolen from my co-worker, Tim (he, however, gives all credit to his wife Christine who bought him his lunch box).
I took my grandfather's old lunch box and added a shoulder strap to it. The shoulder strap came from a messenger bag that was given to me at a conference. The messenger bag was covered in advertisements. Also, the lunch box has the advantage of protecting my gadgets better than a soft sided messenger bag.
The lunch box had a bent piece of wire in it designed to hold a thermos in the top half of the lunch box. I don't need to carry around a thermos and most of my gadgets are actually smaller than a thermos, so I wanted to modify the wire to hold smaller items in the top half of the lunch box.
I grabbed two wire hangers and went cut out the long pieces. I then tied the coat hanger pieces to the thermos-wire, used my glue gun to secure the knots, and then zip tied the connections. The result is a pretty manly looking man bag.