1st you need 2 characters, make sure you have nothing in the first storage slot. 2nd character puts in 1 item that is stack-able into the storage (I put in 1 pebble). Then quit the game and go into the character you want to dupe on. Pick the item you want to dupe that is stack-able and put it into the storage. You either want to use a useless item or buy a useless item that replaces it. Then you get 99x of everything! PROFIT