Whatever you want! When I have free time alone (a scarce commodity) I like to read, maybe have one drink, listen to music.
If it’s not by choice and you don’t want to be alone, go out and have coffee or a drink, watch people.
If you are trying to make it meaningful, do a ritual. Like write down what you want to get rid of, what doesn’t serve you (anxiety, whatever troubles you) and burn it, let it go. A time that’s unusual is a good time to make changes that you want, to interrupt habits.