If you carry a knife with a carbon steel blade (not stainless), the back or spine of the blade can make a great striker. The blade spine produces the best sparks if you file its back edge very flat(so the two edges on the spine have a sharp 90 degree angle). I throw away the included striker and just count on using the back of whatever knife I have along.

Also, a good source for cheap ferrocerium fire steels is a site in Hong Kong called DealExtreme. They have 10 different ones of various sizes ranging from $2.30 to 5.80 all shipped free albeit VERY SLOWLY(expect to wait 3-6 weeks for the item to arrive).