MadOtis

I hunt in west-central Georgia (Upson County) and it does get a bit colder than "the 40's" there, but not nearly as cold as further north. We'll typically get November and December mornings in the high 20's to low 30's... Layering is indeed key. A fairly snug layer of long underwear to help wick away moisture/sweat from your body, an insulating layer (thick tee-shirt and pants [sweats]), then a camo cover tee or button-up shirt is good enough if I'm on the ground. If I'm in an elevated stand, I'll add a layer of insulated cover-alls over the top. I'm one of those people who's feet seem to regulate my body temperature, so, I'll throw a pack of toe warmers in my pack in case my feet start to get cold; if so, on they go; if not, in the pack they stay. Other things to try are fleece neck/head gaiters... if you're subject to getting cold from wind or breeze blowing on your neck, these can really help. finally, gloves... the ones with the built-in mitten flaps are wonderful. Put a chemical hand-warmer pack in the folding "mitten" part... if your fingers get hot, open the mitten; if they get cold, close the mitten.

Also, as others mention... avoiding sweat while walking in does wonders. If you're wearing cover-alls, open them up at the top and/or slip your arms and shoulders out of the top half (use the arms to tie the top half around your waist) until you get to where you plan on hunting. The physical exertion will keep you mostly warm getting to your favorite spot. When you get there and get situated, wait until you start getting cold (this allows alot of the perspiration to evaporate into the atmosphere, thus, not trapping it inside your cover-alls) then put your cover-alls back on or slip your arms back into the sleeves.