Keeping them warm is the key. And don't buy those disposable hand warmers, that can get expensive. Simple dried corn or beans. I used to use a small bean bag size of it.
Minute or two in the microwave, toss it in a small foam cooler with a wash cloth over it. Kept the packs toasty all day long. Also corn or beans when heated give off moisture, the cloth also protected the packs from that.
And as a bonus, when I couldn't feel my fingers anymore, that nice hot cloth was a god send.
I picked up the cooler from the local pharmacy. Roughly 12x12x12 and had 3" thick walls. Was something they had meds shipped in. With the warmer inside, I could leave the cooler outside and the packs were still nice and warm.