My recommended Hand Warmers (works for feet too)

[TooOld2Hike_EP]

I had the chance to try these at Sacramento Pass, NV.

https://ignik.com/products/hand-warmers ... 6615062754

They take a few minutes (15) to come up to temp. But once warm, they stay warm for ten hours.

And, you can turn them "off" by putting them back in their foil pouch. They can be turned back on within a few days to use up their time.

As a bonus, they're small enough that I could tuck them in my socks to keep my feet warm at night. I was even able to position them under the arches in my feet and walk around with them at camp.