The all in one boards, ribbon cables, kits, printed circuit panels, etc. are nice until something in them fails. How many people carry spares?

I still like to source my components, build my own system for the requirements of the car in question. And be able to carry spare parts and easily identify and fix any issue at the track.

I have specific ways of organizing and putting a system together. No kit really fits what I like to do. So why buy it and only use half of it?