To answer Carolyn’s questions:
While a company may try to sell you a gendered pack, you should use whatever works and feels good for your body. Typically, bags marketed to men are taller, skinnier, have longer torso lengths, and have shoulder straps that are more straight, coming more straight across the chest.
You should buy a pack that fits your body, a pack that fits all your gear (plus some extra space for group gear or a sick friends gear) and one that is sturdy enough to last the trip. Most packs that meet those criteria also happen to be ~75 liter backpacks, but you might find yourself in a larger or slightly smaller pack marketed towards a body you didn’t expect. Try them all on, put some weight in them, and see what happens. I’ve carried both “men’s” and “women’s” backpacks on many occasions, and I can share that the fit has more to do with the manufacturer than anything else.
Another one where the marketing may not be accurate. The warmth of a bag mostly has to do with
1. The quality of insulation
2. How much loft it has (height when fluffed a sitting on a floor)
3. Your resting metabolic rate and body composition
In general, a 20-degree bag will have 4.5 or 5 inches of loft while a 0-degree bag has about 6-7 inches. To make up for this difference, a thin liner might not cut it. It’s really hard to tell somebody whether their setup will be appropriate for the cold, especially if they have never spent a night out in weather that would freeze a water bottle. Women, smaller people, and people with slower metabolisms tend to need warmer bags than men, bigger people, and people with fast metabolisms.
When considering your gear, you can ask :
How high quality is my 20-degree bag? Is it really what it says it is? What is the loft? What would it need from a liner to act like a bag that’s 1.5 inches thicker?
Again, usually the answer is either a zero degree bag or your existing, high quality 15-20 degree bag with a fleece liner.
Feel free to get in touch if you have more questions! Gear is a tough one because the only way to fully answer your questions is to use it. Hopefully these guidelines help. We will be sleeping in very cold conditions on our first trek, so warm gear and clothing is essential!