The Palm River Trek Drybag 100L is an excellent multi purpose dry bag which has an integrated padded back pack system.
Designed to be tough and durable and comfortable when fully loaded.
Not only is this an excellent accessory to take on the water but once you have finished your activity you can use it to transport and store your equipment. 
 
Adjustable backpack shoulder system
 
Supple, hard-wearing 420D fabric
 
Welded seam construction
 
PVC Free