How do I clear this list so I can start empty and fresh? Pretty much this.  I'm a bit stuck on getting a decent bake my first time and want to clear the slate and start fresh.
I don't think that there is a way to clear this list without a script. If you don't want to use a script, save your objects individually, and re-load the Blender start-up file. Then import your objects, and make new shaders.