Just got myself a lovely PAC bag, so if anyone wants my old postie bag it's up for grabs. It's nothing amazing, been worn for about 6 months or so, so it's not new or anything, but if you're still carting round the plasticy company-issued square bag because you're too broke to get a proper bag then the postie should tide you over till you get something better.
I installed a clip onto the strap so it's sort of pedestrian quick-release.