I carry spare driveshafts, tie rod, rod ends, U-joints, ball joints, etc. I plan on adding a set of axle shafts also.
Apart from the usual tool kit, I carry a Front End Steering Kit (bunch of pullers and separators) and a U-joint Tool.
My tool kit is pretty extensive and includes just about everything I could need. I also carry a Dewalt cordless drill, Dewalt cordless grinder, and a Ready Welder.
But the odds are whatever spares you carry, you'll end up breaking something else, and the tool you need is the one at home.