Cordless impact is good for going to the track, swapping wheels back and forth but that's it. Still gotta have a GOOD pneumatic unit. Think Ingersoll-Rand at the very minimum. Good torque wrench is a good idea too, again, no skimping (Snap-On, Matco). A good selection of brute force tools like BFH's and good solid prybars can be life savers. Vice-grips. Good screwdrivers. A multi-meter. A good cordless worklight. Nice set of drill-bits. An air hammer. I'm just trying to think of the thinks I couldn't live without other than the absolute basics. Real long reach pliers are nice.
Just avoid cheap crap. You'll just be buying it twice.