Note: This was done in beta version 1.5_01. The easiest way to perform this glitch is to dig a five-block deep 2x2 grave for yourself. Set up the death trap by laying down a dirt block over your head and two pieces of sand or gravel to fall on top of you. Before proceeding, make sure you have everything you want duplicated in your inventory and/or item boxes. Pause game play and wait for the level to save completely, then navigate over to your ".minecraft" folder and locate "saves". Copy the world where you set up your death trap. After copying to a location easily memorable, return to game and walk under the dirt block. Dig it out and let the sand fall on top of you and intentionally die. Do not exit the game. Exit to title screen, then copy the save prior to death back to the "saves" folder. Overwrite everything. Load the game, and you will spawn where you saved before, and have everything from your inventory plus the items you lost via death. This essentially doubles the items you already had. This trick is best used for stackable rare items (Diamond, Gold, Obsidian) and tools made from rare items. Also, death from drowning and death from mobs all work. The main objective is to die after copying your saved game, so that you can spawn at or near where you died to get more of the same items. It may also be useful to fill in your 2x2 space with a large chest (two chests next to each other), so when you duplicate, you can deposit items, repeat the steps, and be able to have plenty of items without the need to hack your saved game file with tools like InvGrid or MCEdit.