Anything you use in bush and doesn't cost a fortune?
I wonder how much money is spent unnecessarily on sharpening kit.
What this guy is saying about that other guy who is saying about that first guy.
You don't actually need to be able to shave with your knife if you're making a tent peg. Quite a few years ago, at the recommendation of the, er, 'technical' department at SOG, I bought a "Lansky Sharpening System" thingy. What a performance. It stays in the box now for years at a time. It cost nearly as much as the knife and it can't even reach the correct angle for the blade that I was asking SOG about -- by about 10 degrees!
You can pick up a wide variety of sharpening stones in many engineering tool suppliers, garden centres, flea markets etc. for a lot less money than in many 'outdoor' suppliers. Here's a random example (about which I make no representations but I'd bet that I could make almost any blunt blade usable with it, even a serrated one, even if I had to break it to do it):
http://www.tooled-up.com/Product.asp?PID=20675
As you can see the people selling it apparently don't know what it's made of. It would be too big for me to want to take it on a trip, similar to the DC4 (but a quarter of the price).
You can bang the rocks together in situ if you really need to make a stone and an old tyre makes a pretty decent strop. I don't know what fuses usually look like in Lithuania but in the UK a cartridge fuse from a domestic 13A plug is usually made of ceramic, like a lot of sharpening stones -- but it's tiny so watch your fingers! You can get much bigger ones from industrial places, ask a friendly electrician to put one by when he comes across one.
I don't know how long you plan to be out on a trip but to dull an edge badly while I'm out camping would take me a week of using the blade quite a lot harder than I usually do. I'd normally avoid using it unless it's necessary, and I'd normally have at least two blades so that I could use one for rough hacking and save one of them for finer work. So I just have a very small, very cheap stone and a 13A fuse in my survival kit. Total weight about 20g. I've never had to use them. I could save weight AND have another backup edge by replacing them with a tiny folder but I would have a small folder in my pocket anyway.