Selecting the proper cold weather sleeping gear can make or break a successful backpacking trip. I try to check the weather predictions for the area I plan to backpack right up until the night before I leave. Thirty (+30) degrees fahrenheit is about the lowest I choose to be out overnight in a tent.
The reason I choose the thirty degree mark is once you start going lower than that you elevate the cost of equipment and the amount of weight you will need to carry.
I choose not to carry any supplementary heaters. Catalytic heaters and such just add weight you that you need to lug around all day. Sleeping bags are available today in the discount stores, but be very careful and take a minute to read the label on the sleeping bag very carefully. I have had friends who bought a $ 39.00 sleeping bag rated at zero degrees and they have half-frozen to death all night at an outside low temperature of +40 degrees F.
Most of the cheap sleeping bags are filled with a synthetic fiber fill material sometimes referred to as hollow fiber. These may be more adaptive to camping down on the farm in the good old summertime, but they lack the ability to keep you warm on cold nights out on the trail. They also are short-lived and do not keep their shape well. So, you could end up with all of the filler at your feet or lumped up in all the wrong places. Common Trade Names are Hollo-fil, Micro-loft and Polar-guard.
I recommend the natural feather fill insulating material. Goose or duck down, preferably Goose. These sleeping bags are generally better constructed as well as being filled with one of the best insulators know to man. They are lightweight and very compact when compressed. They will quickly expand and will keep you well insulated even when they become wet. Compression and expansion are very important. Especially when you are squeezing your bed down to size for carrying on your back all day.
The shape of the Sleeping Bag is a personal thing. I keep two. One is a “Mummy Bag” and the name describes the shape of it. If it will be cold I prefer this bag because it is easier to heat up (body heat) and keep warm due to it's smaller inner size. The larger full bag I use when things start to warm up a bit and I might just want to sprawl some. The shape is up to you.
Another point to look for when purchasing a sleeping bag is a zip collar or hood. These will help you to further conserve heat in the sleeping bag by not allowing body heat to vent out around your head or neck. And, get used to wearing a nightcap (ski cap) it really helps with heat loss.
Sleeping Bags come in many configurations for men and women. As far as the outer shell they are sold in different colors and materials. The main thing to consider when looking for a sleeping bag is the fill material. Get that right and all the other stuff does not really matter.