A few of the larger Swiss Army knives from Victorinox include a plastic magnifying glass. Starting in 2008, this tool is housed in a clear, translucent casing. It's about a 2x lens which is about 1/2" (14mm) in diameter.
Uses: If the sun is shining, you can use the magnifier
to start a fire. Just gather some dry tinder, and focus
the sun's rays on the darkest spot in the tinder material.
The magnifier lens is made of plastic, so be careful not to scratch it. Some people wrap it in a small piece of plastic so it won't be stained or abraded by pocket crud.