I take a lot of pictures out of the window while in flight.

Some people place Windex in a device designed to look like a normally sized highlighter pen. It is actually a spray bottle and fools the TSA 100% of the time. I of course would never dream of making the american security apparatus look like complete buffoons. Anyway, the same people that do this also keep some Brawny kitchen towels handy.

Personally, I choose seat 6A on UA's B-757's whenever I am able to fly in a First class seat domestically (If I am on an international flight and plan to take pictures, I also choose the "A" seat directly in front of the entry door). This gives me the opportunity to clean the window(s) from the jetway prior to boarding the aircraft. I have yet to encounter a problem cleaning the window for row 6 on a 757 when boarding from a U.S. jetway. However, the 777's can sometimes be a challenge depending on the entry door being used to board.