The Meaning of Life, the Universe, and Everything.
I have this suggestion for a API type mod. First of all, It would have layers of clothing. For example, you could wear chain mail over a shirt. Another idea is that you could wear a sheath and or quiver (that doesn't take up an inventory slot) where you could store arrows or a sword (arrows in the quiver and sword in the sheath, of course). This is sort of inspired by lord of the rings like how Aragorn has a lot of sheaths and a quiver. Sorry to be so vague, but this is all I could think of, really.