3M Microfiber Lens Cleaning Cloth
One item I always carry with me when bicycling or camping is a 3M Microfiber Lens Cleaning Cloth. I use them to clean my glasses, sun glasses, bike computer, camera, PDA, GPS or Nintendo DS Lite, anything that is easily scratched.
The cloths are handy because you can use them for cleaning without fluids, the microfibers won’t scratch soft surfaces and clean surprisingly well. They are fairly small, 7 i n x 6 in (18 cm x 16 cm). They last quite a while because they are quite sturdy and can be washed and reused when they get dirty.