Note: To do this you must go to anything that can hold items (a rubbish 
bin, etc.). This example will use gold. Use the "Take All" button to empty 
the bin out, then get the gold and send more than half of it to the bin. 
For example, if you have 50 gold, send at least 26 gold pieces or it will 
not duplicate. Once it is in the bin there should be 26 pieces in the bin, 
and 24 in your inventory. Once done, drag the gold from your inventory to 
the bin, but do not send it over completely. Make sure that the window 
where you can choose how much gold you want to put in the bin is up and 
that the number reads "0". While that window is up, click the "Take All" 
button and take all the gold from the bin. Your gold count should go back 
up to "50" in the number box to the side of the inventory. Then, select 
the "Choose All" button on the gold window. If done correctly, the number 
should read "24". Send the gold over to the bin and the number should now 
read "74" instead of "50". The item will not appear in your inventory until 
you close the bin and re-open the bin or go to your inventory. 
You can do this as many times as desired. The items that this trick works 
with are Gold, Bullets, Fuel, Batteries, and Arrows.