Although Fire Rods and Fire Pistons are very popular with preppers and survivalists, they do have the drawback of either being expendable (as with fire rods), or they can wear down (as with fire pistons). Of the two I would consider fire pistons the most durable, in that "if" you also carry extra seals to replace worn ones you should be able to start survival fires for years. But an alternative survival fire starter is one that simply concentrates the sun to get your fire going.
I'm of course talking about good solar fire starting lens, which with proper care, will never wear out and certainly won't be used up. Assuming there's enough light, a lens can even dry out wet tinder which would otherwise be unable to catch fire. That is a huge advantage, and is where solar fire starter "shines" above and beyond the other survival fire tools.
Obviously, a drawback of any fire starter lens is that if it is dark it won't help. But you should probably be setting up camp before sundown anyway. On cloudy days, getting a fire started with a lens is simply a matter of how much lense you have - a bigger lense should still concentrate enough to start your survival fire even if its cloudy. As a back-up fire starter, you could always carry a fire piston for use on rare occasions.