My proposition: Special Containers. Expand the equip inventory to allow a new type of containers, which expand the inventory menu to hold specific types of objects. (Forgot to draw a keyring, but oh well, you get the idea)

The types of containers I can think of at the moment are:
Key rings
Water skins
Map cases
Purses
I'm not sure that seed bags should count, just because they don't really fit as something that is carried around.