I am slowly re-assembling my vintage Ron Cooper mixte with parts I had on hand.
The past couple of days it was brake cables. The first small issue was that there was a way to adjust the front brake cable with the traditional headtube brake hanger, but no way to adjust the rear brake cable length. Digging through the miscellaneous (junk) drawers I came up with a brake ferrule thingy that I could modify. I had to drill it through and then tap threads to match a threaded cable stop. This may sound simple, but I longer have a drill press and I am ... huh, sight impaired. Half blind. So I felt a little smug when I pulled it off.