I'd like something to touch up in the field or sharpen it back up when I do something stupid. Any suggestions?
Although one of the DMT products is probably better, this little guy could probably be a solution for only $10. A few light passes for touch ups or you could regrind the edge "when you do something stupid". Remember to use light pressure with diamonds.
http://www.basspro.com/Smiths-4-Diamond-Sharpening-Stone-with-Cover/product/1307221115/ Additionally, you could contact cement a piece of scrap leather onto a paint stirring stick and charge it with the buffing compound you use to sharpen. That along with the little diamond stone would be a complete, portable and inexpensive sharpening system. If you avoid "stupid" the little strop will likely be all you need.