The first thing is to work out how much the people in the car weigh, as this will be the first and single largest consideration when determining how much other gear you can carry.

Mating Southern Right Whales, Great Australian Bight,
Head of Bight, Eyre Hwy, SA, en route to Kalgoorlie.

This is the reason why experienced Raiders limit the number of people in the car to 1 or 2.