In the previous post I described how to turn scraps of wood and waste you can't normally use to cook with into usable charcoal. The process that creates this charcoal dust also results in burnable gases that were used during WWII to power vehicles using wood gasifyers. In a world where gas is not available or too expensive to purchase, wood is a viable alternative. The leftover fuel can be repurposed for charcoal to cook, you kill two birds with one stone.
I am not a mechanic nor an engineer there are actual wood gasifyers that are sold to power small houses available for purchase. The gases produced by this process are highly explosive and can detonate with a single spark so if you don't have any kind of mechanical experience or something similar, don't try this at home.
First what you will need is a vehicle without EFI or electronic fuel injection. You need a good old fashioned carburetor equipped vehicle.
Then you will need a 55 gallon steel drum, this will be your fire pit. You will need some way of feeding the fire from the bottom or close to the bottom of the barrel.
Then you will need an airtight steel drum about half the size of the large one, but it must have thick sides and bottom. This will be the gasifyer.
Attach a valve to the lid of the small drum used for allowing the flow of the gases from the burning process. The seal should be airtight around the valve.
Remove the air filter from the carburetor and measure the intake area. You will need an airtight hose or valve attachment to fit over the carburetor intake and long enough to run from the carburetor to the valve on the small barrel. This is where a good knowledge of mechanics come into play, I can't help you with that.
Pack the small barrel with as much wood scrap as you can find, just not so much that you can't fit the lid on the barrel. Place enough wood in the large barrel to burn for twice as long as you need the vehicle to operate. This will take some experimentation.
Light the fire in the large barrel after sealing the small one. Add wood as needed to the fire pit. In about twenty minutes, the gases should be produced to begin driving your vehicle. When you return, use the carbonized remains for charcoal and the ashes for the garden and you will have succeeded in killing three birds with one stone.