* Improve my culinary skills. Some recipes require all day to do "right", and I need to take short-cuts in order to use the 30 minutes - 1 hour I have per day.
* Recreational programming. Few people who are good at numeric programming also have the free time to just "play". Procedural generation, using the latest/greatest visual processing algorithms, automatically integrating real-time data feeds into a "game" of sorts. I hate that I'm using my creativity to generate excel reports that mostly get consumed by programs.
* Music theory. I'd love to know more here.
* Home improvement / homesteading. It would be great to have to time to make my living space better fit for my preferences.
* Volunteering and advocacy. There are a lot of low paying problems in the world that need good motivated minds working on them.
* Art projects. I loved art in college, but never had the time to pursue it in my professional life.
* Personal Health. I love to run and open water swim. Both of these require me to have good weather and be in the right physical state to make use of that weather. Having more free time maximizes my chance to exercise under optimal conditions.
I think it helps that most of these things are things I can do alone and do not necessarily require coordination with other people. The author seems to stress how lonely it is to not have enforced scheduled social time.