I am always worried about losing my important documents like my passport when I travel. So I always put copies of the front page (the one with the picture and personal info) in my luggage. It identifies who owns the luggage and then I have extra copies just in case the actual passport gets lost or stolen. I also have scanned it into my computer and emailed it to myself and usually to a family member as well. That way there is an electronic copy that can be accessed from anywhere if it is needed.
You then can carry the paper copy with you instead of the real one if you feel more comfortable having it around all the time. Then if you have a secure place to lock up the real one you don't have to worry. It is rare that you would need it with you but I have had an occasion when they needed my passport number in order to get into a secure building for the interview I was conducting that day. (And yes - it was both a little disturbing and at the same time super cool to have to get clearance to go in and to sign papers promising to not reveal any industrial secrets based on what I observed. I was finally an important American journalist working on an assignment in a foreign country!)
