i.e. pacman.conf for sure. I think it would be useful to restore a local machine or for a new system, I can copy it and it would be ok.

But fstab, seems to me, no a good idea. Unless it is in a new branch, because every system has it's own fstab but might be helpful to restore in case I need to restore it in my local machine.

What other files would you recommend to backup. I mean, system files on etc folder and the like.