As someone who takes projects to my Dad in a nursing home, and having dealt with nursing homes for a number of years now I will start with commending you for your volunteering. The folks who are in these homes generally are lacking privacy, and mental stimulation is important. Most nursing homes have an activities director who is your first go to person so anything you do will enhance or work into their programs.
My Dad's favorite program was one where a virtual tour of far away places happened. The guy who came up with it would research a country (say China) and find or make a costume that represented a festival or tradition, and show slides and do basically a travelog for the residents.
Then they would have an activity where they made something like a fan or a lantern that fit the country they were exploring with audio visual travel.
One thing my nephew does that Dad does not know about is recording things he gets the old man to talk about since all attempts at getting him to write his memories have failed. This is not recommended to you as there are all sorts of privacy issues if you tried to use any material that it was not very clear you were collecting. Privacy is the one thing folks in nursing homes have a right to, and usually have so little of. There are rules they don't like, people they don't like, and usually they do not want to be there. If you can entertain them you will be a welcome visitor every time.