I like the concept, but why a chest?
It could be a normal human sidekick thiner and smaller than hero, anyway i enjoyed the near 300 miles, meters? played. I like to see more options because as somebody already said it turns monotonous, perhaps after some distance they could find a shop or a town and break the monotony of the same monsters and same background.
I think this game has a lot of potential and can be expanded further. Keep on the good work!
P.S. on a second round i saw the sidekicker is holding a big chest LOL...