In a BoB I would pack one of those cross carbide draw sharpeners. Good for a quick touch up, reliable, and basic enough a novice can sharpen with it. It won't give the surgical edge of other systems, but it is quick, and it will get a blade sharp enough for any sort of field work. Cost about $3.
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The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)