Since this is a broad topic and it doesn't appear to be discussed a lot here yet, what about sleeping bags?
What's really needed? 0? -10? -20? Duck vs Goose? Treated vs Non-treated? Brand recommendations? Assume we're camping in the woods <3k feet.
I'm amazed at the selection and prices - seems good to shop around.
A bag's rating can't be trusted.
If you can open the bag up and observe it before you buy it: If it looks like it's filled with helium - that's a good winter bag.
If it can't support the weight of it's nylon, there's too little dead air in there to insulate you well.
I've mostly winter back-packed. Heat, humidity, mud, bugs and crowds skeeve me.
There's too much good info in this thread to properly quote and give attribution to the poster, so I apologize in advance if it sounds like I'm not doing that.
Winter days are short. Plan on setting up camp at like 2:30. You don't want to be cold, hungry and not set up at 4:30.
Winter nights are long. Bring a Kindle or something. Get up and pee when you need to, it's not going to go away. Or use a large, dedicated bottle in the tent to pee in.
A particular product (tent, bag, stove, etc) won't make or break you. It's a system. Keep and protect (zip lock) a dry set of long underwear, socks, hat and gloves. Perfectly Dry = Warmer in winter.
Use 2 pads. There's no loft in any bag beneath you. I like a decent bag, dry clothes, 2 pads, a small pillow and a bivy sack inside a decent tent.
Eat fatty snacks in the tent. Bring food you can eat even if you can't melt water or light your stove. Know where you're going. It's freaking irritating guessing late in the day.
I generally avoid winter hiking and back-packing solo as it bores me and is a little more dangerous if anything goes wrong.