Here in the east, something I've found that works well is Poplar bark. The woods are full of poplar limbs. After they lay awhile, the bark starts to seperate. It is stringy and fibrous. Actually, it is the fibrous cambium layer underneath.
If you take your knife blade and scrape these old limbs, the outer bark chips away and that stringy inner layer fuzzes up into some fine firestarter. As long as it's dry, one or two strikes from a firesteel is all it takes. I carry a baggie of this in my firekit all the time. It weighs practically nothing. Finding any dry in the rain is a challenge however.
By the way, someone on another thread (or maybe it was this one) posted this link to a GobSpark Armegeddon Firesteel. I ordered a couple and they work great. They throw a shower of HOT sparks. Be advised if you order one the scraper that it clips into is a seperate order item.
http://firesteel.com/gobspark-armageddon-firesteel/