Debian has a distribution special backup directory. Because it is
unique to Debian you might not otherwise know about it. It is the
/var/backups directory.
In that directory you will find the last day's version of several important system files such as password files. You will also find a list of all of the packages installed on your system with dpkg and the status of those packages. This is one of the few directories under /var which would be good to backup. When recovering it will allow you to know what packages had been previously installed. During a recover you can install that same list of packages onto the recovery system. That list coupled with a backup of /etc will quickly allow you to restore your system.