About
Cardboard Box is a custom item made especially for Blackblock.
The cardboard box can be seen as a poor man's shulker box: It has only 9 available slots, and each time you break it, it gets damaged.
Explanation
Cardboard boxes are inferior shulker boxes that have a limited amount of uses.They're most useful before skulker boxes are available, but can be used in later game as extra storage within shulker boxes.
Cardboard boxes can be repaired using your crafting grid like any other damaged item. But make sure your box is empty - like erasing enchants, this technique can erase the items inside!