I'm in that situation already and if you had asked me this question before, I would have said something along the lines of travel, have fun, or some other variation thereof. The reality is while I did do those things for awhile, what I ended up doing was went back to "work". By work I mean grinding on other things of interest to me.
I can't speak for others but its incredibly tough for me to not proactively work on something I enjoy, especially once you have develop the habit of getting use to working a lot.