A good multilayer sleeping bag system is all you need. The ones I used were three layers with the outer layer being a gortex shell. I have gone through cold weather training in Alaska and slept on the ground with only a sleeping bag in -20F and I was very warm with sleeping bag setup. Trick is to get undressed inside the bag and keep your next mornings clothes inside the bag with you. Then you get dressed inside the bag in the morning. My boots were another story though having sat overnight in the cold.