Since your school apparently doesn't award varsity letters, I would be prepared to talk about your RESULTS in whatever sports you participated in. As an example, if you were a distance runner, how often did you qualify for regional or state meets, what place did you finish in those events, did you set any school/district/state records.........etc. Track consists of many events and no one participates in all of them. Apply that same explanation for whatever Track event(s) you were part of. These are rhetorical questions for you to consider, I am not asking you to post your results here.