When I laid down my Yamaha I had a backpack on. However, the only serious injury sustained were to the leftovers from Cracker Barrel I was carrying. I rolled when I went down and the contents of my backpack were crushed. I was looking forward to those chicken and dumplings too.
But seriously, I don't like the feeling of something on my back, so I go the bungie net route on the rear area of my seat.
Sweet bag though, Mike. The automotive seat belt buckle is a cool detail.