i've carried a $10 SpeedySharp in my EDC kit for years.
its carbide scraper puts an instant sharp edge on just about anything, but isn't for someone interested if a finely honed polished edge.
i've used it on tiny swiss knives up thru machetes. even works on many serrated blades (if you follow instructions).
very small, lightweight, tough, never wears out and pretty safe to use (compared to some sharpeners).
http://www.speedysharp.net/