I haven't thought of anything yet.
Left to my own devices, I'd probably spend 100 hours one week programming, then not touch a computer for two or three weeks, reading or building something or doing stuff outdoors instead. Lock me down to 40 hours every week, even weeks when I'm not in to it and would rather curl up on the couch for hours on end with some math books and a notebook or marathon-watch some Criterion movies or go camping with my family or whatever, and any fun I was having in those 40 hours will disappear fast.
It doesn't matter if the thing I'm clocking in to do is play video games of my choice and in the way that I choose, even—I'll be ready to not look at a video game for the next year within a matter of weeks.
That's not to say that I consider all work equally bad, but I'm probably not going to love anything at 40+ mandatory hours every week. The only way I can imagine enjoying that many hours on the clock is by splitting it between at least two very different things, like programming 4 hours/day then carrying heavy stuff at a construction site the next 4 hours, and even that might not do it over the long haul.