When you find a Zombie crate in Blackout mode, it will be locked at first. There will be some zombies near the crate. Kill all the zombies to unlock the Zombie crate. The zombies will also drop weapons and items. The Zombie crate contains weapons that you cannot find anywhere else in the game, unless you kill someone who obtained the weapons. There are multiple Zombie crates that can be found throughout each Blackout game.