Sydney Residents Help!

So now I face a dilemma. As we are off to Slipknot on Saturday I thought we would stay in Double Bay. Close so we could drive. Now I have been informed that WaveAid will be held in Moore Park on the same day. So there is no way we would get a park- WaveAid starts at 10am, Slipknot at 10pm. It's fine to get a taxi there but how are we to get back. WaveAid is expecting 40 000 and I don't like our chances of competing with all these people for a taxi. We could get a bus to the city but how do we get back to Double Bay? Help!
I have resorted to drinking alcohol at lunch to reduce the stress of it all!