The problem of storing a knife securely and easily accessible while keeping it sharp is solved ingenously by the sheath. Sheaths can be made of pretty much whatever you have, but I have come to prefer this type of birch bark sheath. I find it's ability to hold the knife and protect it's edge at least as good as with a "traditional" leather sheath. It is very sturdy, doesn't become limp from moisture and is first of all easy to make with limited materials.
Birch bark is a very handy material; supple, yet strong. For this project you don't need very high quality bark. But it is worth will be easier to make and the results will be more even if you have better bark. Here (Trondheim) the bark is generally of rather poor quality compared to further inland, but you have to do with what you can get. But keep in mind that the bark sheet must be of at least 4 times the finished lenght, 5 if you want to fit a regular belt into the loop.
If the bark has been dried first, the bark will have to soak for a while to become workable. The first you do is to cut strips of bark. This can be done with a bone knife, but is easier with flint. A guide to make the strips even will make the job easier, but I managed without this time. Make one of the strips, the body, about twice as wide as the knife you want to fit into it.
This picture shows how the "body" is folded. One of the ends is longer, to accommodate the belt.
The weaving is started by inserting one end between the front layers and taking a full turn around the body and enter between the back layers.
When on the other side, enter the gap between the front layers and repeat the process until you are at the top. Tighten up the thing while working upwards. If the strip happens to be too short, do not dispair. Simply splice it between two layers and continue. The splice doesn't need to be more elaborate than that the strips rest ontop of eachother.
At the top, pull the strip between the front layers and a full turn around the back and tuck it into the only remaining gap in the front. Of course, if the strip is too long it needs trimming.
As already said, this sheath is remarkably durable and I don't see myself making any other type of sheath in the future. At least as long as I am in a place with birch bark. To the right in this picture is the finished result. A nicer speciemen carry my flint knife to the left, but this one will serve it's purpose equally well.
Keep the knife in the sheath while drying it to make it take it's shape. Also, put a stick through the belt loop to keep it open while drying. If you don't: Good luck getting a belt in there!