The Art of Manliness makes a good case for carrying tampons in your camping/survival kit, with ten woodlands uses for them, ranging from sterile field dressing to kindling to blowgun-dart fletching. They call it "Tactical Adventure Medical Preparedness Outdoors Necessity (T.A.M.P.O.N.)."
Yes, I have a tampon in my mouth — don’t laugh! As a last ditch water filter, you can make an improvised Survival Straw from the plastic housing and cotton from a tampon. As you can see in the photos below, just tear off a bit of the cotton and stuff it into the plastic housing. I find it better to leave a little bit sticking out to make the housing pieces wedge tightly together.
Of course, it goes without saying that a tampon might also be useful if you or someone you know is menstruating.