Stop next to a fence or a pole or something, clip out with the foot that still has all the bolts in place, set it down on the ground, hold the fence or whatever for support if you need to, then use your free hand to untie/unvelcro/whatever the stuck shoe, and pull your foot out of it. You'll still need to free the shoe, of course, but it beats the zero-mph crash club. Of course, it's easier to remember a trick like that when you're sitting in front of a computer, than when you're stuck trying to get your foot out of a moving bike.