Aside from the Maps application, the only iPhone app I have that I think might be useful in an emergency is a free app called "GPS Ally" which simply shows your current location and allows you to email it easily (it emails it as a Google map link, using the current latitude & longitude). I figure if you ever get stuck somewhere, you can at least let someone know where you are (a SPOT-ish feature, I guess).

Of course, one other thing I've thought about is looking into some sort of backup power solution for the iPhone, otherwise it may only be useful for a short while if something ever did happen.