There are those who recommend that you must only operate your camera in comfortable climates. In other words if you are uncomfortable then it’s bad for the camera. Let’s just stop with this non sense right there! If we always operated in a mild 72 degrees fahrenheit we would never leave the confines of our air conditioned homes. Can you say BORING? Although there are optimal operating temperatures for your camera the range is very long. Suffice to say if you used your cameras on either end of that spectrum you would be either extremely cold or extremely hot. But often the issue is not actually operating in those temperatures but rather moving the equipment from a climate controlled environment into either a hotter or colder environment. The problems are usually related to humidity. Anytime you go from a climate controlled environment (which tend to be very dry environments) into a significantly hotter or colder environment you will face condensation problems if there is humidity in the air. This often happens when your camera gear has been inside your lovely hotel room or home all night and then you walk outside with it. Be it hot or cold. And all your lenses will likely fog up. So what can you do about it?
One suggestion is to ease into it. But not many of us want to stand near the hotel doorway for 20 minutes as one eases the camera into the outside world. Although a bit of a snide remark here, the suggestion is apt. You definitely should ease into it but perhaps an easier way to accomplish this would be to keep your equipment in your bag for a while and allow the outside temperature to slowly penetrate your bag: either slowly warming up or cooling down the equipment. In the end, the first suggestion is to plan ahead. If you have a balcony you could put your closed bag outside while you prepare for your day. Do beware of thieving squirrels though!
Another suggestion is to keep dry silica in your bag. These are the little white packets you find in new shoes. They are meant to absorb moisture. Although this is great for keeping your bag dry, as soon as you take your cold or warm camera out into the opposite climate you will still have the same problem.
The last suggestion is to not allow your camera to change environments. Although this is not always a practical suggestion it has its merits. At the end of a day of shooting why not just bring your memory cards inside and leave your equipment in the car? Although not the most secure thing in the world to do, this would most certainly work. Perhaps you could put your gear in a cooler/hamper. This would help to disguise the gear ad keep it more secure.
Note: Do be careful with silica as it comes in 2 forms: powder and pellets. If you use the packet with the powder and the packet breaks, it will be all over your equipment.