Have Tasker backup Global Variable Values when doing a standard backup.
This is a pretty obvious one, even if it has to generate a separate file, which would be a good additional option anyways.
Right now there is no direct way to backup/restore Global Variable names and values in native Tasker. A workaround exists via a "Global Variable Backup Task" posted on reddit a while back, but this should really be baked into Tasker to begin with.