HotHands Body & Hand Super Warmers - Long Lasting Safe Natural Odorless Air Activated Warmers - Up to 18 Hours of Heat - 40 Individual Warmers

Hot hands Large activated charcoal heating packs. https://a.co/d/0asKj8UG If you have any extra insulation that is light... like a fleece etc chuck it in the UQ... If they have a sleeping bag instead of a top quilt it will help a little. Adding a wool blanket with the UQ will help. But those hand warmers and sleep in warm clothes are the best bet.