This datapack adds backpacks, each one has 27 slots where you can put all the items you want.
If you want to get an Exploring Datapack try this crafting. If you want to craft colored versions, place a dye in the center of the grid, at the place of the string.
There are some others version of the Exploring Backpack, you can get them by placing specific items in the center of the grid:
Emerald -> Rainbow Exploring Backpack
How to use a Backpack
Place the Backpack on the second hand
Now, check your inventory. That part inside the red frame is the one that will be changed while backpack's open. But now come back to the game.
Now right-click and your backpack will be opened. Now check your inventory.
You will now find the items of the backpack inside your inventory.
Click again to close the backpack or place your backpack somewhere in the inventory. Pls, avoid to drop the backpack while opened. Close it first.