After spending tons of time trying to figure out the best set up for my bike I finally settled on the Jandd Mountain wedge III. I give the product a huge thumbs up! I did have to to mod it slightly to make it work perfectly, I took the metal hooks off and just zipped tied the plastic fasteners right to the frame. Thing works like a dream now.
The bag also carries everything I need for my brevets, I tend to travel pretty light though. Overall I would also recomend this bag especially if your bike can't take a rack.