The Woodland Wipe

In a phenomenon commonly referred to as runners' trots, the intestinal jostling caused by running sometimes creates digestive distress, most generally along the magnitude of explosive diarrhea. For runners, this can cause numerous problems, the least of which may be finding a bathroom. (A more troubling, frequently related problem is adequately cleaning soiled shorts.)
Fortunately, for many runners, a bathroom may not be necessary. When running in the country, there are always farmers' fields into which one can duck inconspicuously for a bit of relief. Or when running trails in a wooded area, there are trees to duck behind.
For the newcomer, such a scenario presents two concerns: first, someone might see; second, what do I wipe with? While I cannot really address the first concern (when dropping the outdoor deuce, you take your chances... those are stories for another day), I can address the second.
Some runners actually pack toilet paper with them on longer runs, or runs where they think they may run into a bit of intestinal duress. I've done this on occasion, but as a general rule, I don't -- by leave no trace ethics, toilet paper can't be left at the scene of the crime, and even if by chance you did remember a bag to pack it your TP with, no one wants to run holding a bag of toilet paper and poo remains. I've even known runners that have on occasion sacrificed shirts or undies, choosing to wipe with an article of clothing, rather than dealing with TP. Even in that scenario, however, an ethical person is left with the pesky question of how to pack it out. Personally, I hate packing things out, so I choose to work with my surroundings.

In a farmer's field, corn leaves actually work pretty well. If they're too dry, they can be a bit abrasive, or if they're just a little bit damp, they work perfectly. In the woods, down leaves work really well, especially in the later fall, after they've had a chance to soften up some, or in the winter/spring, assuming they aren't too decomposed. In the winter, snow is the perfect wipe: it's cool, refreshing, and gives a very clean wipe if you can pack the snow right. The trick with snow is making sure you don't leave any in... because then it melts, and you're stuck with a soggy bum. Really, though, it's a matter of working with what you have around you.
When I lived at the Grand Canyon, I was faced with some interesting choices. True, there were occasions where, while running in side canyons, I had access to leaves. Unfortunately, however, those occasions were few and far between. More often than not, my surroundings consisted of Pinon Pine, cactus, dirt / sand, and rocks. And that was it. I tried small strips from the Pinon, but got a splinter the second or third time, and that was the end of that. I tried a pine cone, and though it was a bit abrasive, it wasn't the worst. I even tried cactus once, removing all the needles I could first, but still... not a good idea. In the end, rocks were the best option. So, rocks it was. Over time, I learned that skipping stones made the best wiping stones as well. And, inevitably, there were occasions when I was left with my hand... be very careful if you choose to wipe with your hand. You do not want to scratch an itch on your face... you laugh, but just wait -- someday you might forget that you've wiped your bum with your hand as well.

Another lesson I've learned: the longer you wait to poop, the cleaner it tends to be. I've learned to wait until I start getting hot, then cold, almost as if I had the flu. Be careful, here, though: it is possible to wait too long. I've done it twice.

Poop well, and poop often. Just don't wipe with cactus.