Agree, getting in a decent workout or ride can make you feel a sense of achievement for the day. If I can get a 40km ride in before work and then find some good tunes to smash out some code between stand-up and maybe another meeting, I'm a happy guy.
Build something in your spare time? Use the cash to prepare for running a small business? Learn other jobs/skills in your spare time and transition to something you might enjoy more? Prepare for a really long holiday with the cash?
I'm in a somewhat similar situation, I'm solving it by applying for other jobs with slightly higher paygrade in a similar environment.
Also I used to be an artist, and I don't think my art is good enough, so I'm paying another artist to redraw my works, then I'll be paying someone to write better texts and then I'm going to publish eventually.
Also looking for a house to buy, just to invest into something meaningful.