Chest

Chest holds 27 stacks, and two placed side by side merge into a double Chest of 54 with one shared inventory. A third in the same line will not join the pair, which is the rule that shapes every chest room: rows of doubles with a gap, or a wall of them turned to face a walkway.

A Chest will not open with a solid block directly above it, and a cat sitting on the lid blocks it too — that is the closest thing vanilla has to a locked Chest, and the usual answer when one refuses to open for no visible reason. Hoppers ignore all of it and keep moving items in and out either way, which is what item sorters are built on.

Three relatives cover what a plain one cannot. A trapped Chest emits a redstone signal while it is open, so a door, an alarm or a piston trap can be wired to somebody's curiosity. An ender chest shows each player their own private contents from any ender chest in any dimension. A copper chest oxidises through four stages for the look of it, and copper golems will lift items out of one and file them into nearby wooden chests.

Chests generate almost everywhere the game builds something, from shipwrecks and ocean ruins to strongholds, bastions and trial chambers, and buried treasure — the Chest holding a heart of the sea — is tracked down with the treasure map those wrecks and ruins hand out. For moving goods rather than storing them, donkeys, mules and llamas carry a Chest on their back; horses and camels cannot.