Reloader's Permanent Marking Pen (Sharpie)
Permanent-formula ink will not rub off once it has set. Besides identifying special individual loads that wind up in pockets, you can permanently i.d. all the your gear. Permanently marks metal, plastic, wood, cloth. We always carry one of these in our kit.
This is an essential tool for the Curmudgeon because he does not want any of his precious loads to become confused with any other loads.