Waking up on an island in the middle of the harbour is an extraordinary Sydney experience. Bring a tent (or just sleeping bags) or 'glamp' in a two-person tent (with stretcher beds) on the water's edge. Non-campers will enjoy the elegant houses and apartments. For self-caterers, there's a well-equipped camp kitchen; for everyone else, there are two cafe-bars.
Creative experiences, like horror-movie screenings and live-music events can add a bit of sass to your sleepover. Note that you can't take alcohol onto the island unless you are staying in one of the houses.