Put your camera (or GPS, iPod, etc.) in a ziploc bag before heading inside on cold days
January and February have been frigid months in Michigan, but that hasn't stopped me from taking my digital cameras outside to snap a few pictures. Usually when I go back inside, condensation immediately forms on the cameras, making them unusable until they reach ambient temperature and the condensation evaporates. Today I ran across a useful cold weather photography tip from Bob Atkins on the Adorama.com site:
You can avoid problems if you seal your camera gear in an airtight plastic bag before you bring it inside. It will then be surrounded only by the very dry air from outdoors. You may get some condensation on the outside of the bag, but the camera/lens will slowly warm up in dry air inside the bag and will stay dry. Self sealing freezer bags work well for this, but any bag which you can seal will be OK. Just be sure to put the camera/lens in the bag before you go indoors. Once you're indoors, it's too late!
I tried it - it works.