You can fill jerrycans up to 20L maximum size at Australian service (gas) stations - but they must be sitting on the pavement, not in any part of a vehicle, that is off the ground.
This is specific fuel company instructions, and if the station operator sees you filling a jerrycan in a vehicle (via the CCTV), they will shut off your pump and advise you over the forecourt loudspeaker, to remove the jerrycan from the vehicle and place it on the ground before they will turn the pump back on.
This technique is no doubt also in place, to prevent fuel spills creating a vapour-laden vehicle, which is an additional hazard to any potential static spark.