The Rucksack is an item added by Camping Mod. It is a portable storage device. It can store 27 stacks of items. The Rucksack can be opened by right-clicking with it. Alternatively, it can be placed in the additional top slot on the right side of the inventory and then accessed in the inventory's Backpack tab.
It is the highest tier of backpack in Camping Mod.
If there are already items in the Backpack, they will transfer over to the new Rucksack.