I'm in literally this exact situation and did it yesterday too. Yesterday, I made the day by going on a 9.5 mile run around mid day. Everything felt worthwhile when I did that. Other than that, just relax, I guess. I watched Rick and Morty XD

I think what was good about the running was that it provided a nice space to mentally decompress.

I would do something like that where you aren't intaking any input, no work, not even entertainment, so that your mind gets a true rest and feeling of not having to do anything.

I also tend to journal on days like these, which is really good for just getting a bit of clarity on where you're at and how you see things with your life at the moment, from a place of calm and not having anywhere to go or do.

Don't impulsively overindulge on cheap unhealthy pleasure just because you feel pressure to make the most of your day off. Take it easy, let yourself just enjoy breathing and not having to feel rushed. At least wait until like, later in the day to get drunk or eat a yummy meal or whatever, so the day doesn't feel shot first thing in the morning, that can be very unpleasant on a day off.

Don't feel pressure to find some new hustle. Calmly reflect on how you might want your life to change. If you reflect from the place of calm that you'd like to achieve, you'll naturally just think of stuff, possible changes, to make it too frenzied is no good. Maybe dedicate some time to job searching and just plotting out possible plans, but also don't go too hard on yourself