You are allowed to carry one bag and a small personal item for travel within USA as per the TSA guidelines. There is a limit on the dimension of the bag. It shall be 25cm by 40cm by 61cm in dimensions. The items which are considered of personal nature are briefcases, food containers, laptops, purses and cameras. However certain items are not considered to be either of personal nature or come under the free carry on luggage. These items are child restraint devices, mobility assistance devices, outergarments, food is disposable packing for consumption in the flight and walking canes or umbrellas. These items can be taken inside the cabin and will still not be counted either towards the free allowance or the personal items.
If you are required to catch a connecting flight in USA, you shall recheck all such duty free items or liquids that are more than three ounces in weight after getting through the Customs. Liquids more than 100 mL shall be amenable to be screened and cleared if these have to be carried on in the cabin baggage. For this reason, these shall be kept in the secure, tamper evident bags (STEBs).
Southwest Airlines allows maximum of 2 pieces of baggage per ticketed customer subject to the condition that the total weight and dimension of each bag shall be 50 pounds (27-28 kg)and 62 inches (152cms) (L+B+W) respectively. Baggage shall be checked in no earlier than 4 hours and no later than 45 minutes before flight time.
There is special provision for baggage of military passengers. They are not subject to excess, oversized, overweight and even two-bag limitations, provided of course that each bag shall not exceed 100 pounds (56 kg) in weight and 80 inches (196 cms) in size.
Excess baggage charges: For any piece over and above the two free allowed pieces, the charges are USD 75 per piece. Overweight items of or more than 51 pounds and less than 100 pounds and oversized items of more than 62 inches but less than 80 inches, the charges would be USD 75 per piece.