RE: Secret to Keeping Warm
On cold days I wear Under Armour leggings and one of they're long sleeve shirts. (Cold Gear. They make different types if you weren't aware)
Over that I wear light weight Scentlok pants and jacket.
Then my over-alls and my field jacket.
Walking in, depending on how cold it is, I wont zip up my outer layer. Once I'm to my spot I zip up. I have a good warm hat too. To stay warm you need to keep your head warm.
Under Armour might be a little pricey but its well worth it. The stuff just doesn't wear out. It's also skin tight so it allows a free rang of motion if your climbing trees or doing whatever.