I recommend Woobies/Poncho liners.

Contrary to the name. They’re blankets that insulate very well. Every American service member who’s been issued one will live and die by them.

https://www.amazon.com/Premium-Life-Genuine-Military-Weather/dp/B001L0VX2W/ref=asc_df_B001L0VX2W/?tag=hyprod-20&linkCode=df0&hvadid=194884170462&hvpos=&hvnetw=g&hvrand=5032089493816353158&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=1018021&hvtargid=pla-315473101596&psc=1

Relatively inexpensive. Can be paired with sleeping bags. All around great to have when in the cold elements. They also pack very small, taking up little room in bags.

Another thing I’d add. These fleece jackets issued to the military. They’re incredibly warm.

https://www.amazon.com/Propper-F549407233L2-Jacket-Large-Regular/dp/B081T6FG99/ref=mp_s_a_1_1_sspa?crid=3GN7OE1U0HX9D&keywords=army+fleece+jacket&qid=1662795955&sprefix=army+fleece+jacke%2Caps%2C112&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExVkVPQzdLNjFGUk1RJmVuY3J5cHRlZElkPUEwNDc1Mzg4M0Y3VkdFM05WMzdPMyZlbmNyeXB0ZWRBZElkPUEwMzY4NjkyMUJWMlNFOFNTOTFNRiZ3aWRnZXROYW1lPXNwX3Bob25lX3NlYXJjaF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl