Carry "what" and "how much" of it on the plane?
This is the grey area. If Customs views your film cache as a "commercial quantity", it will be subjected to GST and importation charges unless you can prove it is not a commercial quantity (and that is the tricky part!). You can buy film here, or its purchase can be arranged for you online by any person you organise it with. Besides which, buying retail film in Australia is quite silly and strictly for emergencies; online has made a severe impact on bricks and mortar dispensing of film and will continue to do so as prices rise.