I just take a firesteel as I just use gas, but adding a disposable lighter as a backup is hardly going to push your weight budget I guess. As has been pointed out, firesteels are not so great for meths so it depends on your use.
Last year I decided to test out my Ray Mears skills and did actually manage to light a real fire with nothing more than a firesteel, a knife and some wood - no ignition aids or artificial kindling. The key was to find some really dry wood and shred it with the knife, then keep it sheltered and shower sparks on it for a good couple of minutes. After that it's a case of trying to build it up before it goes out - not a game for the impatient! It becomes a lot easier if you happen to spot a silver birch tree - if there's any bark which has peeled off it's like paper.
Edited: 14/06/2012 at 14:11