I just use something simple: https://www.amazon.com/BUILT-Gourmet-Getaway-Neoprene-Lunch/dp/B000ECE5WS and https://www.amazon.com/Nordic-Ice-NOR1040-No-Sweat-Long-Lasting/dp/B00WGA9BO8

Cheap, and handles small or large amounts of insulin. Easy to let TSA inspect verifying the ice pack is solid. Does not count as a carry on since it is medical.

Remember that even if the ice pack is melted, this is better than direct exposure all day, and will still be cooler than not contained.

I use the same solution on a beach for several hours at a time. In the car for longer trips.

Active insulin generally does not need to be refrigerated.