I know this is a loaded question just asking for the answer "It depends", but in general, what sizes/types do you find the most useful ???
My shop finally got to the point I can start making some chips, but looking through my tooling, I've found a few basic necessities missing.
Do center drills work as well in a chuck as a taper adapter ???
At least my lathe tailstock & mill both use the same MT2 taper so things like this would be useful on both.