What part(s) have you let go, only to wish you had kept them not long after?

I’ve learned to never sell engine parts. I had a performer rpm Intake manifold I sold.

A set of RHS/Indy iron heads done up by Brian @IMM.
Hughes roller rockers. A Couple carburetors.
a 340 block. Some floating rods.

That **** belongs on a shelf because ya never know when ya wanna throw together another engine. It’ll save ya some decent coin if ya don’t have to buy all that again.