I'm not sure if any of you hunters carry an extra source of glucose for a quick energy fix. I use pancake syrup and give my oversized boy a shot of it about several times during a long search task. The brain needs glucose to function well and if the glucose is used up trying to keep the body warm, there is less of it for the brain.
If a dog is shivering, it is using glucose. Dogs can stay warmer longer if they have an extra source of it, rather then just what is circulating at the time.
I use syrup rather than a solid food, because he has a tendency to puke when given food while working hard.