Frozen Crate

The guaranteed slot pulls from the frozen chest pool, and half of that pool is movement gear. Ice Skates, Flurry Boots and Blizzard in a Bottle all feed into accessories you will still be wearing deep into Hardmode, since the boots line ends at Frostspark Boots. Getting one of those without spelunking the whole ice biome is the reason to fish here. The weapons in the pool are fine for the moment you find them and forgettable after.

The Fish turns up here noticeably more often than it does in the chests it comes from, so if you want one for the collection this is the sane way to get it instead of opening every frozen chest in the world.

You need water inside actual snow, which usually means digging your own pool in the surface snow instead of hunting for a natural lake. Once dug, the spot is permanent, and the same pond starts producing Boreal Crates the moment your world flips to Hardmode.