Yes, a cooler is considered a carry-on bag, provided it adheres to your airline's specific size and weight restrictions (typically around 22 x 14 x 9 inches). In 2026, most travelers prefer soft-sided, insulated "backpack" coolers, as they are flexible enough to fit in overhead bins or under the seat. However, the "coolant" inside is the real catch: per TSA regulations, ice or gel packs must be frozen solid at the time of screening. If they are slushy or melting, they will be confiscated as "liquids" exceeding the 3.4oz limit. It is also important to note that coolers cannot contain dry ice without prior airline approval and specific venting, and they must be leak-proof. If you use a hard-sided cooler that exceeds carry-on dimensions, it must be checked as standard luggage, which may incur additional "heavy bag" or "oversized" fees depending on your fare class.