Are there activities/organizations that impress highly selective colleges?

There are a great number of "urban myths" about this subject. The truth is the best activities/organizations are the ones that you are truly passionate about. If you love sculpture then that is the best activity for you. I would say the more important issue is how much initiative you take to deeply pursue the activity or organization. It's absolutely fine to choose something "out of the box" to pursue, but make sure you are fully engaged in the activity and that you take on leadership where possible. Yes, we've all heard that every college needs a bassoon player, but that may not be your passion. Choose what you love and dive deep into it!