Stackable

Bundles are a fantastic item that let you store partial stacks in one slot.  They work well in tandem with Shulker boxes which have more slots, but fill up with partial stacks.  However, with items like tools, armor, and potions, inventory space is lost because these items don't stack.  Stackable fixes this!

By making a bundle with leather instead of rabbit hide and putting and ender pearl in the middle, you draw upon the power of ender to store items that normally don't stack on themselves in one inventory.