Re-interpreting the question after my first answer: Like haertig, my irrational fear (other than of dentists, birds and fish) is not having what I'm going to need and not being able to make a substitute. Honestly, it's why I don't fly, hate taking public transit or carpooling in someone else's vehicle, not because of any fear of an actual plane/train/car crash. It's also why I have a tendency to over pack.