Void Bag

The bag gives you your Void Vault wherever you are standing. Use it and a short-lived portal appears next to you; open the portal and the vault is there. The bag itself is never used up, so there is no reason to ration it.

The portal is the boring half. The real feature is the state the bag sits in while it rides in your inventory.

Left open, the vault behaves as a second inventory that you never have to look at. Once your main grid is full, anything you pick up drops into the vault instead of hitting the floor, and the pickup text turns purple to tell you it happened. Everything else follows from that: Quick Heal and Quick Buff read potions stored in there, crafting counts the contents, quick stack to nearby chests works, favoriting works, and looting a chest with a full inventory sends the overflow to the vault instead of refusing.

Items that do something just by existing in your inventory keep working from inside it, so informational accessories, the Lucky Clover and the guide books all report normally. Coins stored there can still pay a vendor, and unlike coins in your main inventory they do not scatter when you die, which makes the vault the safest wallet in the game.

Pressing the activate button on the bag folds it into its closed form. Closed, it is only a portable way to reach your storage, the same category of item as the Money Trough or the Eye Bone, and the automatic overflow stops. That is worth doing on purpose when you are farming something specific and want a full inventory to actually stop you, or when you want the excess on the ground.

The recipe wants Bones, so in practice you need Skeletron beaten and the Dungeon open. The world evil boss is the part people over-plan. You have to summon it, but you do not have to win: break a few segments off the Eater of Worlds, or kill a handful of Creepers around the Brain of Cthulhu, collect the Shadow Scales or Tissue Samples that fall, and walk away. In a drunk world it can come even sooner, since Dungeon enemies spawn there before Skeletron dies.

• Weapons cannot reach ammunition stored in the vault, and neither can tools that consume something, so wire for a wiring session has to be in your hand grid.
• The Coin Gun cannot fire coins out of the vault, even though a shopkeeper will happily take them from there.
• Quest fish are skipped by the automatic pickup if your inventory is full or already holds that species. You can still stash one by hand, and a fish sitting in the vault does not block you from catching another.
• Etherian Mana is ignored by the overflow pickup, though quick stack will move it.
• An Encumbering Stone parked in the vault does not stop pickups the way it does in your main inventory.

Throwing the bag into Shimmer returns the evil material your world uses, which in a drunk world flips from one to the other every in-game day. In Journey mode the research entry always resolves to the open variant no matter which one you fed it. The portal is called a VoidLens in the game files, and early builds of it used a darker purple effect closer to the one the Potion of Return uses today.