We recently went to St. Lucia for our holidays. It was quite hot and also fairly humid. With the air-conditioning in the hotel rooms quite cool - the moment I went out with the camera, everything immediatly fogged up - and big time!
I first tried wiping with a cloth - but that just made streaks.
Finally I just waited 10 - 15 minutes for it to go away by itself.
Anybody have any other suggestions?