Flashlight or headlamp. I don't know how many times I have been asked why I "feel the need" to carry a flashlight with me all the time. I usually say "because I am afraid of the dark".

At work, many co-workers have laughed at my headlamp. For some reason the same firefighter's who see no problem with a light on their fire helmet or a headlamp on their wildland helmet think wearing a headlamp on an EMS call is weird... until they want to borrow it of course. I on the other hand believe trying to hold a light between your shoulder and head is dumb, and having to have someone hold a light for you when you are charting is a waste.

Firearms are a close second... and I usually respond with an adaptation of a Pat Rogers' quote "I don't carry because I am looking for a gunfight, I carry because I don't want to miss the opportunity to return fire should I find myself in a gunfight." or "You never need a gun until you need one very badly"