If you booked QF SYD-CNS then you could use the QF airside transfer bus, saving the AUD 7 train/bus fare and also can drop baggage at the int. terminal for the QF SYD-CNS flight. Much more convenient.
As for storing bags, there is a left-baggage storefront in the international terminal at SYD, fees is rather high (from memory AUD 20 a day per bag, varies by size). Unattended lockers have been removed for security reasons, so this is a monopoly. Not much to do around the airport, esp. as public bus service is extremely limited (deliberately, to encourage using the extortionate private rail station at the airport). Gotta love the privatization of SYD airport, it has made things sooooo inconvenient for pax while sooooo profitable for the private companies that had the right connections.