I sharpen my knives on a mousepad and sandingpaper 2000 grid, then I use a leather belt and finally a few strokes on the edge of a car window.
I take a rolled up sheet of sandingpaper with me and use any reasonably flat surface when field dressing.
And I'm going to make a glass rod and get it sanded, just like the edge of a car window to use in the field.
Another thing that works great are these;
http://uk.ardennes-coticule.com/index.asp?id=384

http://www.fallkniven.com/en/shop/de...sharpeners/dc3