A spare bolt is a good investment - several of the most common AR problems (extractor, ejector pin, bolt lugs, gas rings) are on the bolt and replacing the bolt is much faster than replacing the individual components. It is also not prohibitively expensIve to keep a spare and grips like the Magpul MIAD can store a spare bolt in the grip along with a spare firing pin.
Although as long as you can avoid losing parts, I've never seen a USGI pin break. The tip may get eroded after tens of thousands of rounds but that is about it. I have seen aftermarket Ti or TiN firing pins fracture though.