Clothing.
Bike specific clothing is often not suitable for all types of bikepacking. After 4 days of riding, padded shorts lose their appeal as they gain in olfactory impact. I like to wear fairly normal clothes, but they don’t always hold up to the biking or to the cold.
Pants:
I find when riding bikes in the winter, the fronts of my legs get colder than the backs. There have been commercial tights that address this for cross country skiing, but they often lack the taper cuffs that work best for bikes. I also find that most tights fall down when I am riding bikes. I made my tights from windproof fleece in front, and a stretch fleece in the rear. I had initially planned an elastic waist, but decided I would be much better off with suspenders. The suspenders keep my tights from falling down and thus prevent the fabric from snagging on the seat and causing hilarious crashes.
Jackets:
Winter cycling jackets are similar in that a windproof front and breathable back is ideal. Jackets are not as easy to sew as some of the other items, but they are still within reach of most people’s skills. Fiona has what I think is a nearly ideal bike jacket in that the front panel is windproof fleece, while the arms and back are a breathable fleece. This keeps the vital organs warm while airflow to keep dry and not overheat. For cycling, I always cut jackets a little longer in the back and put longer arms on them than on a standard jacket to compensate for the cycling position.
Socks:
“Don’t forget to mention your mom”
My mom loves to knit. A few years ago, she knit me a pair of socks. She wasn’t sure I would like them, and she was pretty sure that they weren’t as good as the commercial socks that I buy.

It turned out that the socks my mom knits are warmer, fit better, and last longer than any socks I have purchased. So if you knit, or know someone who is kind enough to knit you some socks from Merino wool. (lately my favourites are a Merino/Silk blend) I strongly endorse home made socks.
Hats:
I have several store-bough hats that do most of what I want. I am fully happy with them as my day time headwear. For sleeping though, I want something to replicate the hood on my mummy bag when I use the quilt, or even just to supplement the mummy bag hood.