For backpack hunting, a piece of lightweight foam is worth it's weight in gold to sit on while glassing. Keeps the ground from sucking the heat out from you and keeps you comfortable to avoid moving before you should be moving during the crucial early morning and late evening glassing.
I've seen these used, and at 2 oz you don't take much of a penalty:
Thermarest Pad or be like me and cut a chunk out of your wife's yoga mat.
