Generally, airlines allow one carry-on bag and one personal bag per traveler. Additional items such as coats, camera bags, hats, umbrellas, canes, walkers, diaper bags, magazine or newspaper, food items for immediate consumption, small strollers, child seats for ticketed children, and such are generally not counted either as travel bags and will be allowed. That said, try to keep as many of the smaller accessory items in your approved carry-ons to avoid any potential hassles as you hand your ticket to the agent.
While individual airlines vary, as a general rule, the carry-on bag should not exceed 45 linear inches (add up the length, width and height of your bag to obtain the linear inches). The general weight limit for carry-on luggage is 40 pounds. Regardless of your airlines actual weight limit, the bag should be light enough for you to lift into the overhead compartment without endangering other passengers. Most airlines have a sizer box at the gate to determine if you may carry on a particular bag. Even if the linear maximum is not reached, odd shaped bags, such as one that is tall and skinny may be rejected. Carry-on bags must fit under the seat or in the overhead compartment. Overhead compartments tend to fill up quickly on crowded flights. If you'd like ensure your bag will fit under your seat, select a carry-on bag that is 18 inches or less wide.
Personal bags are generally defined as purses, briefcases, laptop cases, tote bags, book bags, or small backpacks. However, on most domestic flights, you are unlikely to be stopped with a small carry-on and two personal bags such as an average-sized purse and a briefcase.
Note: Be aware that the smaller, turbo-prop planes may have quite limited carry-on space. This catches many travelers off-guard who have connecting flights to vacation destinations such as the Bahamas, with the last leg on a small jet or turbo-prop plane. What may be allowed on the first leg of your trip may not fit when you switch planes for your final destination. Review your itinerary before you pack to see what types of aircraft you are scheduled to be flying aboard, as this can help you make smart carry-on packing decisions.