Perishables

Delta allows you to carry perishable items such as fresh or frozen foods, fruits, vegetables, meats, fish, poultry, bakery products, flowers, cut flowers, floral displays and vegetable plants in the aircraft cabin as part of your carry-on baggage allowance, provided no agricultural rules are violated for the destination country.

If the item does not meet size or weight restrictions for carry-on baggage, we will accept the item within your checked baggage allowance upon completion of a limited release form. However, Delta will not be liable for deterioration or spoilage of any perishable item contained in checked baggage, whether with or without the knowledge of Delta.
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I think the cooler still has to conform to less than 50 lbs and no more than 62 inches length+height.