Stingaree of some sort Urolophus testaceus? the Common Stingaree
A Strong Fish, also known as a Dusky Morwong
Yelloweye Mullet Aldrichetta forsteri
A nudibranch. I have no idea what sort as there are too many species.
PS. After writing the blog entry I spent nearly all of one evening on the very informative Sea Slug Forum pages hosted by the Australian Museum and it seems our little friend is the fairly common: