If you don't have something specific in your past that makes for a compelling example, I think it is best to focus on your future. Admissions committees are impressed by people who know why they want an MBA and who understand how an MBA will help them achieve future goals. Playing Division I sports has very little relevance to business school or one's success at business school. But, this type of experience may show perseverance, drive, teamwork skills, dedication, leadership, etc. So, your job is to show that you also have those skills.

You have probably heard a great deal about creating a "memorable profile" - this may be easy for the athlete or soldier ("oh, yeah, I liked that guy - the one who was Lacrosse captain") but it is possible for anyone ("remember that guy who hates pasta? he seemed really interesting"). You just want to create some personal way to differentiate yourself (preferably in a good way!).

PS - I went to Booth, and, while there were a few people who may have had some "extraordinary" experience, most students were regular people with good experience and solid future goals. All were interesting and accomplished, but, basically, just regular people!! You didn't need to have published a book or started a company to get a spot in business school - those are the things people did afterwards!!