JAF,
I prefer convexed blades/edges. Once you learn the techniques for maintaining a convex, it's hard to go back to a beveled edge. For field sharpening a convex, I carry a couple sheets of wet/dry sandpaper in my wallet and I wear my strop - the back of my leather LL Bean field belt with a 3" section of the belt charged with stropping compound. If you want to get really fancy with your finish, carry a 3 - 4" piece of brass rod in your PSK to burnish the edge when you're done sharpening.
Here's a great link to a convex sharpening tutorial...
http://home.nycap.rr.com/sosak/convex.htmM