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How much carry-on baggage can I bring?
Carry-on baggage is a small piece of luggage you take onboard the plane with you, and is subject to a maximum outside linear dimension of 50", for example 10 inches in length inches x 16 inches in width x 24 inches in height, be under 30lbs/14kg and must fit in the overhead bin or under the guest seat. However, if the item does not fit under the seat in front of you, it will need to be light enough to be safely lifted up and placed into the overhead bin. 
Guests are allowed one carry-on in addition to one personal item such as a handbag or pocketbook, coat or wrap, umbrella or walking stick, camera or binoculars, briefcase or laptop computer case, infant bag, infant/child safety seat used to transport the infant/child.  (If the child has a reserved seat and will be using the safety seat during the flight, it must be a Federal Aviation Administration (FAA) approved safety seat.)
For detailed information on what you can or can't bring, it's a good idea to check with the in the US for more information.