David West loves his Nicholson cross-hatched file. As he says, you can pick one of these up for about a buck in a flea market. After that, you need WD40, a good side grinder and drill, some paracord and some patience. Yes, it’s a lot of time for a very basic tool – but when you need a flint and steel – you want to know it will work!
SAFETY FIRST: these are metal files throwing off sparks and bits of metal. Don’t take any chances with your skin or eyesight!