At the farm where I used to work there were more than a few sheds filled with all kinds of junk - about a hundred spare tires, cans of old diesel, big loops of barbed wire, broken implements, and on and on. The stuff was kept around 'just in case' but generally took up really valuable space. So I can definitely see how you'd want to keep the clutter to a minimum!
To keep the grass down in certain areas, we laid down tin roofing, and then covered it with wood pallets. The bottom layer could be done with a tarp, although that would be flammable, and they degrade in the UV over time. Anyways, if you are going to keep the spare car around, and if fire is a concern and you can't cut the grass beneath the car, doing something like that may be an option.
To keep the grass down in certain areas, we laid down tin roofing, and then covered it with wood pallets. The bottom layer could be done with a tarp, although that would be flammable, and they degrade in the UV over time. Anyways, if you are going to keep the spare car around, and if fire is a concern and you can't cut the grass beneath the car, doing something like that may be an option.