A caution about using body heat to keep equipment warm: You also emit a lot of moisture along with the heat. When you put a cold object in your clothing, moisture is likely to condense on and inside it, possibly causing it to malfunction. Using waterproof versions of the equipment or placing them in sealed (eg zip closure) plastic bags before putting the device in your clothing can help. (This is the same recommendation for bringing cold equipment into warm rooms.)
FWIW, Canon gives their underwater cameras (eg D30) a 14F minimum temp rating and all of their other cameras a 32F minimum temp rating. My guess is that this is due to the risk of moisture freezing inside an unsealed camera.
Note that batteries and most electronic equipment can be carried cold--they only need to be warmed up when used. (Minimum storage temps are usually lower than minimum operation temps.) One exception: LCD displays that get really cold can freeze and crack. (The minimum storage temp depends on the LCD. LCDs designed for outdoor use (eg GPS displays) generally have wider storage limits than the LCDs used on non-outdoor equipment.) Check your spec sheets for both the operational and storage temp ranges.
Doug