That’s what I’ve done, while canoeing in Algonquin Park and running into an un-predicted heatwave with temps around 100F. I wet a T-shirt in the lake, wrapped my insulin, put it in a plastic bag, and kept it deep in my backpack. When it seemed to be getting even hotter, I also put the plastic bag inside my bag of flour, because I’d remembered reading that flour acted as an insulator, though I don’t know if that’s true. No guarantee it would work in the jungles of Nicaragua, though!