Stockade Crate

Locked Gold Chests in the Dungeon are one and done, and the Golden Lock Box inside every crate is the way around that. If you want a second Muramasa, a Cobalt Shield for a friend, or another Handgun to push through Shimmer, fishing is the only source left once the Dungeon has been stripped. You still need a Golden Key for each box, but Dungeon enemies keep handing those out, so keys never become the bottleneck.

There is almost no standing water down there, so you build your own pool. It only has to sit deep enough inside the brick and background walls that the game still reads the spot as Dungeon. Skeletron has to be dead first, and nothing Dungeon flavored will bite until he is. Before Hardmode the same hole gives you the Dungeon Crate instead.

The ore and bar lines look more generous split across four rows than they are in play. A single crate rolls at most one kind of ore and at most one kind of bar, and it will never mix an early metal with a Hardmode one inside the same category. Two draws, not four.

Mostly building material. Books pile up fast if you are putting a library together, the colored Dungeon bricks cover a themed room, and the painting pool is the least tedious route to the Dungeon art without sweeping every corridor by hand. The bait line quietly matters, since Journeyman Bait and Master Bait coming back out keeps the farm feeding itself. The potions are ordinary crate filler.

Once you have Shimmer access these turn into their pre-Hardmode counterpart. Both crates carry a lock box, so what actually changes is the table around it, which is only worth doing if you specifically want the earlier loot pool.