I have been using the Icebreaker Hand Muff for years.
http://www.icebreakerinc.com/php/hanblanket.php
I don't even use a heat pack or wear gloves underneath. I'll tie it around my waist, that way if I stand up or take my hands out to take a shot, it doesn't get tangled in my bow or rilfe sling.
You can usually find these at Gander Mtn. for about $20. Well worth it IMHO.