If you find yourself without matches and you need to build a fire in the wilderness, simply use the lens of your eye glasses to reflect sunlight onto a small pile of kindling (bark shavings, pine needles, and dry leaves).

As the intensified light ignites the kindling; add more wood. You can also do this with a magnesium fire starter: a few magnesium shavings can be ignited with a spark from the "sparker" on the device. These can be purchased for around $5 at Wal-Mart.