The problem is that warm air can hold more water. If warm air in fact does have a lot of water (i.e., higher relative humidity) then cooling the air will cause the water to condense and form fog that will result in water droplets on cool surfaces touched by the cooling air. Note that warm dry air does not cause the same effect. It has to be full of moisture.
Consider a camera at 70F inside that is taken outside where the air is full of moisture and at 100F. The air that touches the camera is cooled to some lower temperature, and at the temperature where the amount of humidity becomes 100% of what air can hold, moisture starts to condense and fogs your glasses, your lenses, and the camera.
The solution is to prevent warm moist air from coming into contact with the camera and lens until those items warm up to a temperature where the relative humidity is below 100% (probably within 4-5 degrees of ambient air temperature, though it might be less on really muggy days).
You can wrap your camera in a coat, put it in box, seal it in a steel drum or waterproof bag, or whatever. Those will all work but all have a serious disadvantage that they also insulate the camera and cause it to take longer to warm up. The best solution is to put the camera into a kitchen sized plastic trash bag, and squeeze out virtually all of the air. Then place the camera/bag in a place where it will warm up fast (good air circulation is helpful, for example).
A very viable alternative is to put the camera into a regular camera bag, close the lid, and don't open it until the inside of the bag is up to ambient temperature. That is the easy way, but since the inside of the bag is well insulated it is also a very slow process compared to using a kitchen trash bag.
Notice there is no value to putting a desiccant into the bag with the camera (there's no extra moisture inside the bag). There is also no need for the bag to be air tight either, merely avoiding significant air exchange is sufficient.