Injuries

RPM rucksacks are better for your shoulders..

Courier type bags will put uneven pressure on you, unless you can counterbalance it with a massive chip on the other shoulder.

You can get one by riding in London for more than five years, or being a Courier for two weeks ;)

and the sh*te thing is the bag's on my left shoulder! so annoying. I dont think i could hack it as a courier unless i do some serious training.