I'm particularly enchanted by the annual Accio Books campaign. And I love that the different houses compete to see which can collect the most books. (Ravenclaw was the winner last year, which seems appropriate somehow.) The whole thing just sounds like fun, collaborative work to make the world a better place.
If you're interested, you can donate, join a chapter, or volunteer.
I love seeing fans come together like this. I love the hope and the optimism … and I'm always happy to see how stories can inspire people to change the world for the better.