Personally I rate the figure-8 over the bowline. I think it's a much more versatile family (and much easier to tie and inspect with high confidence soaking wet in the dark).
Good point! I think I mentally chucked it with the square knot under "knots that should already be in most people's inventory" but you are right, that is definitely worth learning, since there are so many useful variants.
So like, 4 essential knots: Figure 8, square knot, bowline, hitch. The map, filter, fold, and reduce of knots, if you will. Most everything else can be composed from those.
Square knot most people already know. Tautline and bowline are the two worth memorizing being able to do soaking wet in the dark.