Sacks (which can store 5 items like a shulker box) can be placed inside bundles from Bundles Plus to create an item more overpowered than a shulker box that can store 320 item slots in one inventory slot.

Needs confirming:

• Do sacks inside the bundle hinder the player?
• Can bundles be placed in sacks, creating an endless loop of infinite storage slots?
• Is it intentional that the Bundles from Bundles Plus don't display a GUI like in 1.17 vanilla?

Confirmed:

• Sacks in bundles do not hinder the player
• Endless nesting of sacks and bundles