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

70 RT/Se Challenger
Extra SE challenger rear window/insert
Complete factory 6-pak from a 340 with air cleaner
Heads from a GT 390 FE engine. Ports were similar to a 427 medium riser I think.

Didn't sell my left leg to buy a 68 GTX vert for 4k back in 86.

The list goes on.