Like many others:

• Work on my free time tech projects out of passion
• learn new languages
• play videogames and consume a lot of movies and series'
• Travel my heart out, and not only via planes. If I actually had a lot of free time without the need to check in somewhere, I would just fill a backpack with all the necessary stuff and travel to my destinations via trains, hiking, renting a car, etc. since time would not be an issue
• Just be... while sitting somewhere outside, might move sometimes to another spot
• Actually meet new people. I don't because I feel like I barely have time for my current friends. That is so god damn sad that I alienated some of my friends due to work and keeping up with closer friends. Fuck work.

Edit: sorry for the rant on the last point. I know not every job is like that and I'm in the process of switching my field.