Diy Heatpacks

[diburning]

I am shipping a fish out on monday and I ran out of heatpacks. I cannot order heatpacks and have them delivered in time.

I went around to pharmacies and drugstores to look for heatpacks but it is a little early so none of them stock them yet.

Is there any DIY way to make one?? I will be overnighting the fish so it doesn't have to last more than a day.