I played with a couple friends in a band, although it was pretty informal. It might be worth mentioning, however, that we did throw a charity show for a friend with cystic fibrosis to raise money for her to go to Tanzania to work at an orphanage. It wasn't through any organization, though, and it was a one time thing
If you have something more tangible like that then maybe its ok to put it down. If you say that you've just fooled around in your room with it a few times not so much unless perhaps you were learning for years and just play for fun. I know its confusing but my point is, it should be somewhat significant. Otherwise more generalized hobbies like just strumming a guitar or going to the mall if that is your hobby is something you put when specifically asked about that not in a resume thing. That's how I feel. I feel like the activities section is a resume essentially.