Oh.... stretching! Probably the one thing most walkers don't do enough of. You should be stretching every hour for 5 minutes. Basically at every pit stop you should spend 5 minutes stretching. While the big "walk" muscles need to be stretched (calves and hips), don't forget the back and shoulders too!
Also look for stretches you can do on the route. A stop light is a great opportunity to stretch those shoulders. The more you stretch, the better your body will feel.
Also take some time once you get to camp to use the yoga mats and do a good full body stretch! :)