The problem: Painting stuff without removing it from the car. You know, that linkage on the carburetor needs some color but you have to do it without painting the carb itself, the intake manifold or valve covers. Or, maybe the panel holding the radiator could use a coat of paint but it's too much trouble to remove the radiator, hoses, brackets, etc. Maybe you're dyeing the door panel and need to mask the handles, or touching up a small area of the dash. Using newspaper and masking tape is difficult, time-consuming and frequently lets overspray through.
The solution: Aluminum foil. Everybody has a roll of this inexpensive, versatile product. It "forms" itself over any shape easily and quickly. Masking tape sticks very well to its edges, without the nuisance of cutting newspaper and trying to hold it while sticking a strip of tape to its edge. Also, aluminum foil works great to cover carburetor intakes, generator/alternator air intakes, A/C compressors and all the other stuff you don't want to get wet when you clean your engine.