I just take some 3F and grind it up in a mortar-and-pestal. Any NON-SPARKING surface will do. Do about 20gr. at a time, away from the main supply. That way if for some dumb reason it does ignite, all that'll happen is you'll singe a few hairs on the back of your hand!
I usually just use 3F to prime the pan when out in the field. Doesn't seem to matter much.
