A duffel bag is a flexible option if you don’t want to bring a rolling suitcase as your carry-on, depending, of course, on what you’re packing. While it may vary from airline to airline, the maximum duffel bag carry-on size is typically 22 x 14 x 9 inches for flights within the U.S. Bag size limitations on international flights can vary, so always check ahead of time on the airline’s website.