I know this is has been requested several times and I know there are third party scripts (I use one) but I think it would be a great openWRT enhancement to have the ability to backup the list of user installed software and then have the ability upload that list to re-install those software packages.
This mostly applies when we perform a sysupgrade. The configuration files get backed up (via backup) but not the list of additional software I have also installed (wiregaurd, vnstat, USB, filesystems, etc).
opkgscript.sh writes to /etc/config/opkg.installed, which is automatically backed up, so it is available after a sysupgrade.
if you include opkgscript.sh in your sysupgrade.conf, then the script itself will be available after a sysupgrade too. You just need to run it and you're done.