Good 12v air compressor

To an extent, "powerful" and "12V" rarely go together for air compressors. Viaiar 12V compressors are generally well-liked and seem to be among the best available. They have several models of varying capability and duty cycle and price.

If you have a generator or a decently sized inverter, a small 120V air compressor may be a practical option and rather easier to find. I carry a Fini AirBoss compressor, ca. $100 or less on sale occasionally from Lowes. I've been quite happy with it so far for typical class C needs (like topping off tires). It would be hard-pressed to do much with, say, an impact wrench or die grinder.