Learn a new skill

It could be anything - learn a new language, learn how to cook well, learn to paint, probably start composing music, anything that you ever wanted to learn but due to lack of time or resources you refrained.

Now is the time because you have ample of time for yourself moreover learning something new improves underlying neural circuitry may eventually improve the quality of life for individual.

You also learn to apply solutions from past experiences to face fore-coming challenges while learning new skills.