I used to carry a small, medium grit, diamond hone (see link), but more recently I optimized and carry a Leatherman Juice XE6 in my kit which has a small diamond file among a variety of other useful tools. It wouldn't be optimal, but it could get the job done.

Diamond hones are nice for this kind of task because the diamond coating is fast, lends itself to small, light sharpeners (since it is only a coating) and is very long lasting with the light use that you might see in a kit.

Phaedrus, I agree that it is much better to sharpen at home, but I do think there is a use case for a sharpener. Basically if you are forced to use your blade in a way that damages or significantly dulls the blade, you want something better (faster) than trying to use a rock to repair it.

As long as it doesn't take much weight/space, why not?

FWIW, I feel the groove type sharpers not only don't do a great job, but can be harmful to the blade and try to avoid them unless I have no other options (in other words, never :-)

-john


Leatherman Juice XE6 (small but complete multi-tool)
http://www.leatherman.com/product/Juice_Xe6

Eze-Lap Diamond Hones (small, lightweight diamond hones)
http://www.amazon.com/Eze-Lap-Diamond-Hone-Kit-Sharpeners/dp/B000HDXDDG