[deleted] The classical are /tmp, /run, /var/tmp, /var/log, /var/spool, /var/run, /var/lock
Personally I don't backup /var at all, if you need stuffs under var (like for instance /var/www if you installed a web server for your developments, you know you want to backup it).
Regarding your initial post, many things don't apply for vanilla Solus (i.e: /opt, /usr/local, /var/backups, /var/local, /var/games, /var/mail, /srv, the crontabs things, ...)
Also I find this weird to advise to backup /var/lib there is nothing you want to keep there. You should backup your data, not applications or libraries that can be reinstalled.