Edit: When you spawn your pocket is 9 placeholders wide.
IDEA: The portable chest backpack.
When you create a chest you can place it back into the crafting bench to do so:









THE WOOL SERVES THE PURPOSE AS ROPE.
The chest model itself is a half-block.
TO PLACE ITEMS INSIDE YOU MUST FIRST PLACE THE CHEST ON THE FLOOR.
WHEN FINISHED YOU DESTROY/COLLECT THE CHEST AND PLACE IT INTO THE INVENTORY.
It appears on your back when done so.
Edit: This addition gives you the the 27 placeholders you already have inside your inventory.