When I am afield, I don't remember the last time I didn't have a short 6" bastard file. I primarily use it to resharpen my broadheads, but I've used it on a roughed up knife, on axes and so on.
The rock I used isn't flint I know that for a fact. I don't really know what the make up of it is but it works like a dream.
Some pictures and a video below. The stuff I used to make the new char cloth are breast pocket flaps from an old warn out cotton canvas field shirt.
File, stone, wasp's nest, some char cloth and other goodies in there. Finding pieces of wasps nest is always a bit of good luck. Makes a great material to blow a coal into to get a flame.
Close up of the squared end on the file and the stone I'll be using.
Set up and getting ready to spark it.
Video of sparking and blowing the coal to flame in the wasp nest tender.
Charring in action.
Finished char, turned out real good.