It's always good to have a few spare bits, especially things that are harder to find/don't show up often, or especially if they may be used on multiple bikes (like a transmission). I've got a set of carbs, a transmission that still needs its input shaft replaced but is otherwise good, a final drive, starter, a rear wheel, and assorted cables and some electrical bits that I've replaced but which were still operational. It can get out of hand, though. I am hoping to get another early 80s airhead of larger displacement, and many of these parts (and others) can fit multiple models (except the LS-specific wheel, etc.) Having some spare electrical bits that may be used but are still working, such as an ICU, voltage regulator, or bean can can save you on a long trip or help save a fellow "airhead" who may otherwise be stranded for a while.