I pack my LowePro MiniTrekker backpack in the Happy Trail top box (14X22X7) along with a Gitzo Traveler tripod. Have enough room left for the GoPro kit and a pair of sandals! The backpack does a fair job of keeping things from shaking apart.
Current pack ready for the CDT includes:
Canon 5D MkII
Canon 24-70 f2.8L
Canon 580 EXII Flash
Really Right Stuff flash mount and pano gear
Pair of Pocket Wizzards
HyperDrive portable hard drive
Misc. cables, memory cards, chargers, etc.
Tank bag will have a Leica DeLux4 point & shoot for the quick shots. Plan on doing a fair amount of time lapse and pano with the DSLR on this trip so I'm stoked!
01 Jeep XJ w/ 200,000 miles as of 3-26-11