Here's our definitive answer: Take Capri Sun packets (equal weight to fish as in 1 pound fish, 1 pound Capri Suns), remove straws and freeze the packets. Get any Igloo cooler that is as least 2/3 inch thick. Layer fish and Capri Suns in cooler. Make sure to place a thermometer in the middle and one at where the fish meets the Igloo. Seal with tape and lots of business cards. Drop off at check in. We've found from past baggage delays that the fish/igloo thermometer will read around 37F after 40 hours (i.e. a one day baggage delay). Good luck!