Little Smith's pocket steels are great for field touch ups. A small stone can do alot it just take a bit more time. Scandi grinds are my favorite for in field touch ups. A convex grind on a big chopper I'm not worried about until I head home and can use full size equip.

There are some great dual grit diamond "stones".

http://www.dmtsharp.com/products/duosharp.htm

One of the 8 inchers with fine and medium and you would be good to go. They are thin and don't weigh much at all really. You could put many many sharp edges on a blade.