Back in the steam-age and vacuum-tube days of yore no gentleman would dream of leaving the house without a freshly laundered cotton or linen handkerchief in his pocket. And when not being used in its (somewhat disgusting) intended role as a portable and recyclable mucus container - the good old hankie provided a convenient duster, sunhat, arm sling, tourniquet, and ad-hoc bandage. Us modern-day day chaps, being less likely to be punched in the nose by random cads, can get by with its high-tech equivalent - the microfiber cloth.
I always take along a microfiber cloth, especially if I'm going to be away from home or office for more than a couple of hours with my devices.
The good thing about the microfiber cloths is that they can be incredibly useful for cleaning OTHER things: Things like my sunglasses, computer monitor screens, the lens and viewfinder of my cameras, the screen on my iPod Touch, the rearview mirror in my car, or the face of my (analog, mechanical) watch.
Microfiber cloths safely remove all but the most stubborn smears and grease, along with dust and stray hairs, from just about any sensitive shiny surface. As long as you don't use it on items that can pick up grit or other abrasive matter, you can move it from device to device without worry. Gently launder every month or two or as needed.
