step 1) put items in a chest
step 2) press esc so that the world saves
step 3) open the chest, and without ever exiting the chest:
step 4) put the items back into your inventory
step 5) exit out of the window causing the game to crash
step 6) open the world back up and you will have duped
If it doesn't work the first time, because it messes up sometimes try again. This works for alpha 1.0.0, also called infdev-20100630-2 but may work in other versions.
![](https://s2.save4k.ru/pic/0t_-g2Eq1bY/maxresdefault.jpg)