I have a little system that I put in my go-bag for carrying fishing line:

I cut a pencil down to a length just a tiny bit shorter than a film cannister. Then I epoxied it to the center of the inside of the lid, and further epoxied a little plastic plate onto the other end of the pencil, thus making a spool with a pencil for the spindle. I would it up with 10# fishing line until it would just barely fit back into the film cannister. It's a sort of self-contained system as the spool snaps right into the cannister, and there's always the pencil in there if I absolutely need a writing utensil.

If this isn't a clear description let me know; I could take pictures but it's so simple once you see it there really is no need for a complex set of instructions.