You really need very little to survive, as your flatmate knows. When I was a student, I lived happily for six months with just the contents of a large backpack. Another time, my husband, children and I lived for two years with just the contents of four suitcases while the rest of our stuff was in storage. Did we need anything else? Occasionally, yes, but not that often and like you, I forgot most of the things I’d left behind. In fact, I felt happier with less — and cleaning and organizing was much, much easier, saving me time and energy.
Enjoy living in Sydney — it’s an awesome city!