Chest

Every chest placed during world generation rolled its loot at that moment, and nothing afterward changes it. Entering hardmode does not reroll a single container. A chest you walked past in your first hour holds exactly the same thing a hundred hours later. There is no reward for saving exploration until you are stronger, and no reason to hesitate about emptying everything the moment you find it.

Depth and biome pick the pool. A surface chest carries one item actually worth having plus a scatter of starter filler. Go deeper and the headline item improves, but the filler works the same way underneath: the game walks a set of groups, checks each one once, and takes at most a single entry from it. That is why you never open a container holding two items of the same category, and why a good chest tends to feel like it has a theme rather than a random pile.

Gold chests close to the floor of the map pull their filler from a nastier list, the same one that feeds a Shadow Chest, so a run along the very bottom of the caverns is worth more per container than the same effort higher up. The Lava Charm narrows it further. It only turns up in gold chests sitting in the lava layer itself, the stretch of cavern where open pools start appearing, and being down there also pushes the other headline items down in probability. A lava layer sweep is a specific trade, not a general upgrade.

Gold chests in the dungeon are sealed and want one key apiece. The dungeon supplies its own answer: every plain wooden chest down there carries a golden key, so clearing the cheap containers funds the expensive ones. The biome chests deeper in are a different problem, since their keys are rare drops from the matching biome rather than something lying nearby. You can also seal your own storage with a Chest Lock and open it again with a key, which is mostly a multiplayer tool.

Pyramid gold chests follow the same height rules as any other for their filler, so what you get partly depends on how deep the pyramid punched. In Celebration Mk 10 worlds they stop being a gamble entirely. The pharaoh outfit is guaranteed, and so is one of two mobility items: usually a Flying Carpet, and failing that a Sandstorm in a Bottle instead. That turns finding a desert in those worlds into a dependable early jump in movement rather than a hope.

A container holding anything at all cannot be broken, and the block underneath it inherits the same protection, which is the usual explanation when a floor tile refuses to give. Empty it first. If all you want is a different look, block swap changes the style in place and leaves the contents alone.

Taking the natural chest with you after looting is worth the extra second. Your map stays honest, because any chest icon still showing is somewhere you have not been. It also removes the ambiguity that gets people killed, since an untouched container sitting in a corridor is exactly what a mimic is imitating.

Turn one into a Trapped Chest and it gives up storage to become a trigger, which is the cheapest bait mechanism in the game. Leave it as normal storage and run wire to it instead, and a signal makes it hoover up loose items lying nearby, which reduces a farm's collection problem to a timer pulse. Town NPCs refuse to sit on furniture with a chest beside it, so lining a house with storage quietly ruins the seating. You can craft directly out of an open container, so a work bench next to your material stash saves an enormous amount of shuffling. And out of the whole sprawling roster, the Golf Chest is the only one anybody sells you outright.