I don't think it is so much important what you do, but how you can show that it makes you a well rounded person and a desirable employee e.g. commitment, initiative, responsibility, time management, team work.
This year my ECs are:
Mentoring youngsters in Rotherham
Tutoring Y6s in literacy
Spanish tandem for second year
Debating (love it!)
I also have a couple of slightly unusual hobbies I can talk about.