you can dupe items by using them from inside a container (protection case, medkit or ammo box, maybe clothing aswell)
- Legacy ID
place a usable items (e.g. a bottle of vitamins) in a container (medcit or protector case), place the container on the ground. empty your hands, then use the item from the container while its on the ground. the item will be used and if its not used up it will be placed in your inventory while a duplicate remains in the container on the ground. items that would normally be used up (e.g. blood test kit) are simply used but not used up, they remain in the container.