A journalism professor of mine threatened once to randomly stop you on campus, and if you did not have a pen or pencil on you, to flunk you for the semester. His contention was you never knew when you'd encounter a story, and should be prepared always to write. To this day, most of the time, I have a pen in my pocket.
October of 1989, I was without power in my apartment for two days after Loma Prieta earthquake struck San Francisco. Only a few days before I'd spent almost $20 for then new Maglite AAA flashlight; the smallest, most powerful flashlight I'd ever seen. It was my sole light for two nights. Since then I have spent a small fortune on powerful pocket flashlights. The most recent is the brightest yet, and only $3 at my auto parts store.
And what self respecting geek like me does not have a USB drive on them at all times with common software tools?
Its easy to get carried away. Small tools don't take up much room in your pocket and can be a big aid. A few small items stack up, so I always carry less than I want, and more than I should.
Not as bad as a guy named Eric who carries 1300 items in his jacket. As he says, "I simply saw that there are many problematic situations that could be avoided if you had some usual objects."
I do enjoy keeping my travel kit lean and mean, with every item being useful on just about every business trip, and rarely running into a need on the road I have not anticipated.
Eric's inventory is useful in choosing items to have. Another person who never leaves the house without everything he might need is Batman. One enterprising fan has compiled a list over every item Batman has pulled from his utility belt in comics, cartoons and movies.
Maybe this compulsion is why I like Smartphones and Tablets. Think of all the tools they compile into one item. Map books, GPS, flashlight, stop watch, alarm clock, TV guide, Weather radio, TV, radio ad infinitum.