Welding Gloves
Might sound strange, especially if you don't plan on welding anything, but a pair of the $10, or less, welding gloves you can pick up at markets are very versatile. You can pick up and fit a hot exhaust that has dropped off, lift a heavy object without cutting into your fingers and grab the can of bake beans out of the fire and hold the can while you open it and get a feed. Move hot logs around the camp fire, work on a  fan belt on a overheating engine and some other things I haven't yet experienced.

Thick Shade Cloth
A decent piece of thick shade cloth to be used as a ground sheet is a must have in my view. My own piece is a creamy coloured item, thicker weaver than the stock green stuff and I use it to place under the tent or swag. It keeps the dirt from your feet and out of the swag and the tent and stops twigs and dirt from attaching to your feet.
Also can be used to roll under a Moke for mechanical work/check ups and keeps the dirt out of the grease and parts and for longer roadside repairs, someone ele's can be used to prove shade on the sunny days.

Silver/Grey Tarp
No point taking one of those cheapy blue tarps you normally see tearing itself to shreds on the back of trailers. Autocheap and some hardware stores sell heavier duty a silver tarp with a black underside and rubber reinforced corners for a around $40 and they are a much better investment. Again can be use as ground sheet for camping gear  like a swag can be rolled up to keep dry in heavy rain or pull over the top if you are trying to sleep in the rain. On nights likely to see frost you can cover the Moke to save having to wait for the windscreen to defrost in the morning.

300W Inverter
If you are traveling with electrical gear like a Laptop, Electric Shaver, Digital Camera etc then a decent 300w 12v to 240v inverter for around $100 is a good option and normally can be used while driving to charge items up and flatten your battery at night if left plugged in and switched on.

Drinking Water in Cask bag or small Bottles

Trying to carry all your drinking water in one large 10-20lt container can be difficult to store and contamination can ruin all your supply. Better options are to use 2-3 lt orange juice bottle, bladders from wine casks or even just buy your drinking water in the casks at the supermarket or stock up on bottle supermarket water in the 1.5 containers. All give you more options for storage, can be refilled without risk of contaminating the remaining supply, and are normally handy to drink from.
I usually take a few 1.5lt bottles and then when empty refiull them from a couple of 5lt casks of water.
In a Moke drinking water while driving is important to keep you hydrated as the openness of our cars mean you lose body fluid much quicker than being in a Boring Vehicle.

Zip Lock bags
A pack of 20 or 40 that are a bit bigger than the sandwich size can come in very handy for storing the roll of toilet paper, the shower soap, the washing powder, yesterdays jocks, food wrapped in paper, items like cameras you want to keep the dust out of, spare parts.

Toilet Paper
Even on a  trip where bush camping is not expected carry a roll of your favorite wiping paper as Mokes don't always breakdown in the most convenient spots, travel conditions change and sometimes dictate where you will be needing to go. Public toilet paper is not always going to be to your butts liking either.

Octane Boost
If your Moke needs 98 Ron fuel then you need to bring your own Octane Boosting additive as outside of the main towns is going to be 95 at best and sometimes 91 is the only unleaded available. If you have a 'performance' engine you might consider turning back the ignition timing to make the vehicle more friendly to 95 or 91 fuel. Another option is to caryy a 20lt can of 98 fuel and use it to mix in the fuel tank when the only the lower fuel is available.

Tyre Air Compressor
Not a requirement for everyone to carry one but the more amongst the group then the less demand and quicker we can re-inflate the tyre after sandy patches or returning to the bitumen. I don't think much of the little $30 AutoCheap compressor and prefer my $100 4wd option which is bit more robust and quicker. A good pocket tyre gauge is a good investment to make sure your tyres are coming back to the same pressures each time and don't rely on the guages on the air compressors.

Fire Extinguisher
Every Moke should carry a little 1 or 2kg extinguisher handy for the unfortunate times when they may be needed. Make it easy to get at and not under the drivers seat or anywwhere it can come loose and hinder your driving while on rough roads or knock you out in an accident.

Wet Shoes or Boots
A pair of Gumby's or at least some old shoes that can be stored in a bag filthy with mud and not your good driving moccasins. I have a pair of rubber slip on shoes, called wet area shoes, that I use for walking on water(barefooting) but are also very good for walking through a creek crossing to check for obstacles. Crocs are good too.

Handwinch and Snatch Strap
Not something everyone needs to carry but at least one of each amongst the group will come in handy if conditions require it.

Jaffle/Waffle iron
I carry very little in the way of cooking items, ie no gas bottle or stove, but I have succumbed to buying an old style waffle iron to cook up some bacon and cheese snacks in the camp fire. Quite versatile, can do eggs, and takes up very little room.