If you are going to carry a knife in the field, you should probably carry a knife sharpener too. The GATCO Scepter 2.0 Serration and Knife Sharpener has a few features that might make it ideal as a field sharpener.
The Scepter 2.0 has a pull-through style tungsten carbide style sharpener at one end that can help keep a working edge on your knife. The other end is threaded with a removable insert. The insert has a tapered diamond sharpening rod that can be used to sharpen serrations and be removed to reveal a ferro rod type fire starter. The addition of the fire starter allows the Scepter 2.0 to replace 2 pieces of gear.
Check out the GATCO Scepter 2.0 at Knife Center.