How do I modify the debug menu--add custom items?
For some reason, feathers aren't spawning or being collected when ducks are hunted. I'm trying to make a rugged village, and want to make feather+reed coats. 

I noticed the debug menu has 9 slots for "add custom items to storage areas". When I click them (custom01, custom02 etc), nothing spawns in the storage, so I assume I must somehow select what these custom items are. How do I do this?

I want to make one of them feathers.

Thanks in advance!