On American Airlines, you are generally permitted to bring both a backpack and a duffel bag into the cabin, provided they meet the specific "Personal Item" and "Carry-on Bag" size requirements. In this scenario, one of the bags (usually the backpack) must be small enough to fit completely under the seat in front of you; the maximum dimensions for this personal item are 18 x 14 x 8 inches. The other bag (usually the duffel bag) would serve as your carry-on and must fit in the overhead bin; its maximum dimensions are 22 x 14 x 9 inches, including handles and wheels. This policy applies to almost all fare classes, including Basic Economy, which now allows for one free carry-on in addition to a personal item on all routes. However, if your duffel bag is particularly "stuffed" or oversized, gate agents may require you to check it, especially on smaller regional aircraft where overhead space is limited. It is also important to note that if you are traveling with an infant, items like diaper bags or breast milk coolers do not count toward your two-bag limit. For a stress-free boarding experience, ensure that your backpack contains your essentials and fits comfortably under the seat, leaving the overhead bin for your larger duffel.