ES DID leave a comment in regards to warming up a camera in a plastic bag.
Since some of you may not go back and read comments, I thought I would share it here. ES is a photography professor so I am confident with his advice;
I would not put it in a sealed bag...mainly because it will actually trap any moisture. And moisture is the enemy of anything electronic.
The temp change issue really will only manifest itself if the equipment sits for a long time in a super cool dry A/C room then one goes outside into a super humid warm enviroment. And even then it will really only affect metal-bodied equipment and glass. Most consumer grade cameras have many plastic parts and this is unlikely to be a problem. Pro cameras and lens are metal but they are weather-sealed (as someone mentioned) but still susceptible to the A/C -humid scenario mentioned above on the glass elements.
In cold (esp extreme cold) the things to watch out for is keeping your battery warm and respecting your camera's temp operating range. You need to pay attention to this because the oils inside may not handle extreme cold. And cold also depletes the battery.
Bottom line, I doubt you will encounter a problem if you simply enjoy your camera sans zip lock bag.