Marathon running and backpacking as extracurriculars?

I'd try to look at this experience from different angles and try to find something unique.

I mean, many people run marathons. I live in a place where it's snowy for 5 months in a year, and I even made myself to train enough to finish an Ironman. Still, thousands of people accross the world do finish Ironman triathlons, including those who work long hours, have no sports participation experience, have three kids and work as CEOs of large businesses etc.

True, it's a great accomplishment for every individual - and you are within a rather scarce bunch of people if you compare it to 6 bn people around the world. But I guess, in a subset of business school applicants marathon itself doesn't distinguish you enough. So worth mentionning, but not a subject to make it a key topic, I guess.

Still, you could take a broader look. Do you have some good results? Did you lose half of your weight after deciding to train for your first one? Did you motivate lots of people to run? Did you volunteer at local events to promote running, and maybe have some evidence, incl. statistics, numbers etc. on people you actually helped to?

My personal opinion, of course.