The crate is a large wooden supply box designed to carry heavy loads of items and materials; these boxes were possibly knocked or thrown overboard passing cargo ships.
Players are able to interact with washed-up crates - while they cannot be placed in the player's inventory, they can be destroyed to acquire the item(s) held within. Different items have varying chances of spawning out of broken crates.
As it is an unofficial addition to the game, the crate can only be obtained through modding. Whether it will officially be implemented in the game has yet to be announced. Should it be added to the game, it is speculated that crates will be found washed up on the shore at a random time of day.