If you want to steer clear of a toilet emergency, limit caffeine and avoid greasy, spicy or sugar-free foods before a run. Choose bland, low-fiber—and, dare we say, constipating—foods instead. Bananas, low-fiber cereal and applesauce are all easy on the stomach.
Once you're out on the run, bring a bit of emergency toilet paper and have some restrooms mapped out. If you're running with friends, let them know that nature is calling. As fellow runners, they'll likely understand! Ask them to do loops around your bathroom of choice so they don't have to interrupt their run.