I forgot collecting and plopping down huge barrels from magic pockets.
They are called a Bag of Holding in D&D and even that rare and powerful magic item doesn't make it possible to use potions from someone else's inventory, or the entire party using the same Greatsword +1 to attack while also using a shield during enemy turns.
Also with a Bag of Holding, in 5E it holds 500 lbs. A barrel in 5E is 70 lbs, and holds 40 gallons of liquid. If that liquid were water, that barrel would be ~400 lbs, meaning that you could only get one barrel of water in a bag of holding with about 100 lbs left over.