If you remember anything about knife sharpening, let it be this: A harder surface can sharpen a softer surface. Find a material harder than your knife, and it’s possible to hone an edge.
As this video points out, common materials can be used for knife sharpening in a pinch. Car windows, rocks, other knives and more are demonstrated. One not included, but cited often for alternative sharpeners, is the bottom of a ceramic coffee mug.
Learn more about the science behind sharpening in this knife maintenance download from BLADE, a sister publication.
And if you prefer more modern sharpening systems, Gun Digest recommends this 5-Stone GATCO kit.