I think minimalist solo diving depends a lot on how and where you dive, and your personal experiences.
Where I solo dive there is a lot of speed boat traffic overhead, so I always make sure than I surface near shore where my buoy is located (we are not permitted to tow our dive flag buoys, by law).
It is also completely dark below 60 feet, so lights and backups are necessary. The terrain is rather featureless and the visibility is less than 10 feet, so you can't navigate without a compass.
Once I ventured out solo and my one compass failed. I found myself at 100 feet in complete darkness with no idea which way back to shore. I could hear all of the boats zooming overhead.
After that - two compasses, two of everything.
Where I solo dive there is a lot of speed boat traffic overhead, so I always make sure than I surface near shore where my buoy is located (we are not permitted to tow our dive flag buoys, by law).
It is also completely dark below 60 feet, so lights and backups are necessary. The terrain is rather featureless and the visibility is less than 10 feet, so you can't navigate without a compass.
Once I ventured out solo and my one compass failed. I found myself at 100 feet in complete darkness with no idea which way back to shore. I could hear all of the boats zooming overhead.
After that - two compasses, two of everything.