My local Sportsman's Warehouse has these Smith's(tm) knife sharpeners for about $4 or $5:



I tested it on a few dull kitchen knifes (one high-carbon, one stainless). It put a workable edge on both of them in no time. I don't have the heart to draw my brand-new RSK Mk1 through it, but it's to be a field expedient sharpener, not an everyday sharpener. It weighs in at about 1.6 oz and measures 2-1/4" x 2-3/4" x 7/8".

Using a hacksaw and a file, I put it on a diet:



It seems as easy to use as before. It's less bulky and now weighs about 0.9 ounces. I drilled a new lanyard hole (if there's anything I've learned here, it's that everything must have a lanyard hole). I'm going to toss it in my backpack until I find something better. But for $5 and not much elbow grease, I'm happy with how it came out.

Disclaimer: I frequently do things that make my friends wonder if I'll live another year. For all I know, I've made this sharpener unsafe. I don't think so, but could be. Please use your good sense and don't get hurt.