He should be fine for a few hours.. but if you are worried about it, I would go to a drug store and pick up those little handwarmers and leave one near his deli cup (just don't let it touch the deli cup because it'll be too warm for the snake).
I usually bring a cooler with me and place the snake inside (in it's container) along with a warm water bottle and a towel to make sure the bottle doesn't come in contact with the snake container.