I originally heard that term coined by Grant Petersen of Rivbike and I whole heartedly agree. I like to be completely self sufficient when I'm out riding so that requires having the right gear with me at all times.
That would include a tire repair kit (tube, patches, tire levers), multi tool, lock, camera, food and a place to store clothing as it gets removed while the day heats up. In the past, I would carry everything other than the tire repair kit, in a small backpack. The repair kit would be carried in a small underseat saddlebag. I don't like using a backpack on my bike, especially when the weather gets hotter. Instead, I've attached a rack to my bike and have modified a set of equestrian saddlebags to fit the rack.
For the rack I have chosen the Streamliner Road DLX from Axiom.
I wanted something narrow that followed the lines of the bike's seat stays.
The saddlebags attach to the rack with leather laces. I had a shoe repairman insert the metal eyelets.
The laces are simply tied inside the bags.
The saddlebags mounted to the rack.
A nice match with the Brooks saddle.
What could be more appropriate for a Saddle Up bike than an actual pair of saddlebags?