You have to soak fatwood for a looooong time before it won't light. The best stuff is literally dripping with pitch/resin. Water beads off it. You can get it to soak up water if you leave it for in the wet for weeks.

I don't generally have flares with me, even the small ones. They're pretty bulky and take up space that I would rather dedicate to fatwood and ESBIT tabs. I always have UCO Stormproof matches in a waterproof container (with extra strikers), a couple lighters and a ferro rod.