Dusbuster minivan, we bring a whole spare front subframe...that means whole front suspension, engine, trans, axles, hubs, etc. It is actually tidy way to make sure you have everything
1947 Plymouth, we bring a spare trans if traveling more than hour from our home base, coils, CPS, hubs, and not much else. L67 engines litter PnP's. We will likely bring the spare engine with supercharger to High Plains but that is because it is more than an hour to fresh water let alone a junk yard.
1999 Esteem, this is a one and done car for us but we want to win the IoE with it so it has to run all weekend. No one stocks anything anywhere but regional distribution centers for 1.6L Esteem. We have bearings, hub, CPS, Coil, wires, MAF, spare from pads and we other things that would sideline us if they go bad. IT was $153 shipped from rockauto so cheap insurance.
Without old Saturn...spare subframe again because we could swap the subframe in about an hour in track conditions. That is faster than most teams (including ours) could swap an alternator on one of those when it is hot.