I am currently filling in my Common App activity list. I have already listed nine good activities, but I cannot decide which activity I should list as the 10th. Here are my options: (1) AwesomeMath camp, (2) 100km hiking in Qaidam Basin, and (3) being a contributor on Math StackExchange for 5 months and now I have about 400 reputations.
I had listed a better math summer program so the first choice is less preferred. I am not sure whether (2) is an activity. (3) seems not quite impressive but I really like it.