In a pinch I use a soft tissue and just a dab of water...gently rub the screen to wipe off dirt / dust.
Careful about tissue, it feel soft to you but the wood fibre in there is harder than plastic and scratch will show if you have the smooth LCD, same goes for polycarbonate flashlight lens and eyeglass.
I just cleaned mine with Mr. Muscle window-cleaner, before I saw this thread. Sounds like the sort of stuff Sgt. LED would approve of.
I'll let you know if my screen dissolves as a result of this, lol.