Chocolate and a Soda Can
Yes, seriously. You can start a fire using a soda can and a chocolate bar. I can't take credit for this one. I saw it on an episode of Mythbusters.
Use the chocolate bar to polish the bottom of the soda can. Rub the chocolate on the bottom of the can and use a piece of cloth to rub it again the surface until it's polished. The surface will be shiny and reflective once it's been properly polished. You want it to have a mirror surface. Don't give up too soon. It can take as long as 45 minutes to get your can polished to a mirror surface.
If you have steel wool, you can speed up the process and use it instead of chocolate.
Once it's polished, pick up a piece of tinder. Hold the can sideways in your hand and tilt it back and forth until you get a good focal point on the tinder. The focal point will be between 1 and 1 ½ inches away from the bottom of the can.
The tinder should light up in no time at all in bright sunlight. Transfer the smaller piece of tinder into your tinder bed and use it to stoke your fire.