I've been running these engines for many years, and I've never had a injector suffer a sudden failure. I'd had them get to where there is a lot of white smoke at start up, a trail of white smoke at idle, and I had one stick and started "knocking" on a truck that sat a long time (I bled it and it stopped) but I see no reason to carry around a set of spare injectors. They usually give a lot a warning. If anything, I may carry one spare if I was a nervous type, but there's no way all of the injectors are going to fail all at once on a 6.2/6.5. The chance of a sudden failure is WAY higher with the IP than the injectors.