The Drop Item block will let you only allow certain choices when the user drops item/s or gold coin/s. It can be accessed through the thirteenth button in the add block buttons area.
When clicked, a new block will be added with the following inputs:
How many items need to be dropped;
How much gold coins to drop;
The text of the choice presented when items/gold dropped;
The node to jump to when the choice is selected;
Create a new node to jump to when the choice is selected.