The reason I didn't include self-defense is because the questions involved there have been pretty well gone over on any number of forums and in any number of books. Plenty of people carry for self-defense on a regular basis and their reasons for doing so are well documented. The question of other survival situations I don't think has been dealt with as thoroughly.
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A gentleman should always be able to break his fast in the manner of a gentleman where so ever he may find himself.--Good Omens