I voted for all but None.
I keep spare kits for all my firearms, spare barrels too, basically everything to get the thing going again in case of most of the common parts breaking. Springs - all, Firing Pins/Strikers, pins, Mags (and spare followers and springs too). Replacement sears, and trigger components, extractors and ejectors , gas pistons for rifles, recoil buffers, yada, yada yada. Unless the Frame and Slide, or Lower or Upper receivers crack I can rebuild pretty much any gun I own. I also have spares for any aftermarket stuff too.
I consider it important to have spares for most of the stuff I own that I'd like to keep operating especially those things that could be life critical.