Environment
I have a standard Ka bar that I got years ago. It is really unused so far. All I did was treat the leather sheath and grip with neatsfoot oil. Keeps the leather parts from drying out or shrinking. And they look better. The blade is coated carbon steel so it is protected. The edge is bare steel but it was touched with some rust preventative and is still perfect. I have stored this knife indoors, in the original box. Nowhere near any moisture or excess humidity. You may get rust in a sheath, if you carry it in the field that way, or store it say, under a car seat or in the trunk. I cannot see it ever rusting in a home environment around here, like in a closet or drawer. Don't sweat it but you will have to take care against rust on exposed carbon steel in the field, except maybe in a very dry climate. You could grease it and put it in plastic, or such, if you thought it would be exposed to elements anywhere outside the home. Man, alot of people have a thing for old socks for guns, knives, etc!