I plan to include academic activities in areas other than math (computer science in particular) and a single line titled "hobbies". (One professor suggested that I should demonstrate interests outside of math because that makes me less likely to burn out and crash, but I should be careful not to let random activities detract attention from my academic pursuits.)
That being said, if you have some really outstanding accomplishment that's unrelated to math, it might be worth mentioning anyway. Coincidentally, a friend of mine raised a fair bit of money for charity and was accepted to applied math programs that seemed out of here league academically. I don't know if her fundraising efforts were at all relevant to her admission success, but I wouldn't be surprised if it made her application more memorable. (That, and it demonstrates initiative and networking skills which are important for professional success as well.)
That's assuming that you are applying straight out of college. If you have been out of school for a while, you certainly want to explain what you have been doing in the meantime!