During the gap year, you could do either paid work or volunteer work (does not need to be “charity” work, many libraries have volunteer positions, for example). Of course you could do a mix of both.
However, the main focus of such a gap year would be to do additional research on colleges; especially ones with excellent merit aid for students with your stats. Perhaps funds from paid work would allow you to visit the colleges you find most interesting. Personally, I would never attend a college that I had not visited (remember that such visits can happen after acceptance). Also take some time to just do a few things you enjoy, like reading books that interest you, or hobbies that you might have neglected.