Just to follow on to what Sam noted above, my goal when flying is to carry on everything that would be irreplaceable (or too expensive) to replace/borrow while at the race. As such, I take radio, cars, batteries, and bodies (if I have space.) I figure that I can always borrow tools and a charger from someone else if my checked bag is lost or delayed, but all of the above items are too difficult/expensive to replace at the race.