A glitch that results in duplicating weapons and containers requires two people. One person is holding a gun in his hand while another gun is behind his back. He logs off from the server and second person then quickly handcuffs his body, the weapon instantly drops to the ground and then uncuffs the person so he wouldn't die next time he logs in. The first person still has both of his weapons in his inventory and there is a duplicated weapon left on the ground that his character dropped after being handcuffed/uncuffed.

Same method is used (I believe) duplicating containers held in hands before logging out, but the character has to have all his inventory filled and no spare slots (or no more than three slots) so that container wouldn't be brought back to his inventory.

Sometimes container disappears from the ground, so the second person doing handcuffing has to quickly pick it up before the first person's body disappears.