Rada and/or Spyderco Sharpmaker.
I like that Spyderco setup.
The hardware store sells a little pocket/keychain version, I think made by Lansky. It has a carbide V on one side and 1/8" ceramic rods on the other side. The carbide is good for sharpening a hoe or shovel, in a pinch, but I only use the ceramic on my knives.
Heck, I often put a shaving edge on my pocket knife or a hunting knife using the unglazed bottom and then the glazed side of a ceramic coffee mug. But if one struggles to hold the appropriate angles when stroking the edge, the V sharpeners are fool proof.
added: google Lansky quick fix knife sharpener. I see one listed at $7
