Since I'm not into totally PC (though I've tried to get more towards at least correct), I never authentocated it. But I carry a small whetstone in a sheath I made from scrap elkhide in my shooting bag. If that's all I'm carrying, I want to be able to sharpen my patch knife. I'd think a file would be a handy thing to have in a possibles bag, though a bit much for my shootin' bag.
crocket, any knife that is constantly wheted will eventually get worn down. I've seen head knives worn down lopsided and mis-shapen due to frequent wheting. Fileing will obviously do it faster, but just using stones will do it just as sure. And most of the old timers when I was a kid were fanatics about sharpening their knives.
When I was a whole lot younger, I worked as a ranch hand with a 73 yr old Dutchman straw boss. He'd look at my pocket knife right after I sharpened it and say "explative, you cud ride to Europe on dat thing." There's no fanatic like a German fanatic in charge of a ranch operation in close to wilderness conditions.
Dan