This slot is currently empty, and bait piles up in inventory. How about an offhand box for bait?
Make it craftable by armory or blacksmith (Not sure which one needs another item in their list) and have the number of slots increase as it's level goes up.
From a programming point of view there is already a bait GUI in the fishing menu. And I'm guessing the mechanic from the armory chest could be used. So it would probably not take very much "completely new" code.
Thanks