Simpson Trip

Without wishing to trivialise your question Stuart, the best spare you can take is another vehicle. Not sure if this is your plan but if not I'd recommend it. It makes the trip more enjoyable and certainly takes the edge of some of the potential risks of breaking down in the Simpson.

Having said that, from past experience, I'd recommend spare belts, spare radiator hoses and spare tyres as the absolute necessities. You will probably have to lower tyre pressure, so some form of tyre inflation device will be required once you get to the end of the dunes.

Plenty of water and if travelling alone, you should consider hiring a RFDS HF Radio. Don't forget to log your trip with police at Mt Dare or Birdsville and sign off after the crossing. These days, it can be a bit busy so take care as you hit the top of the dunes (a flag on a high pole on the bull bar helps)

I am sure others can contribute more to this discussion. It's a great trip, take the time to enjoy it. If you are camping in the dunes one night, take the time to walk to an adjacent dune away from camp fire and lights and you'll see stars like you've never seen before.

Safe travels.