An item cloning glitch that occurs on LAN worlds when multiple accounts are used.
1. Create any singleplayer world on Account 1.
2. Log out and log back in on Account 2, and load that world. Account 2 will have the same items at Account 1, and will spawn where Account 1 logged out.
3. Open the world to LAN and log in on another computer on Account 1. Account 1 will have the same resources and will spawn where they logged out.
4. Enjoy double items.