The addition of a simple carabiner clip has made my Carradice Bike Bureau bike bag much easier to use. It lives on the carry handle and holds my shoulder strap out of my wheel or off the ground when the strap is not on my shoulder:
It also is pressed into service carrying my cable lock. This has been invaluable whenever my bag has been over-filled (which happens more often than I should admit!)
The best part is that it's designed for easy clipping and un-clipping so I don't mind it at all. Digging my lock out had been a drag. No more!
UPDATE: Looking at this post I was struck by how aged my bag looks. Here's how it looked in a photo from 2005.
