Your gonna wanna use a 72 hour heat pack or a long lasting Ice Pack depending on the temps to and from when shipping, check your weather before hand. Always wait as long as you can before bringing them to USPS, FED-EX, UPS, etc.. the less time in the bag, the better, And you already know this but OVERNIGHT SHIPPING is a must with Fish.
Try to make it so there is a good amount of air in the bag, always double-triple bag if possible if case 1 bag might develop a leak, and last but least, package with lots of crushed up paper or packaing peanuts to lessen shock (outside of the fish bag of course)
