Many airlines will accept a rucksack as a personal item, and if they do, the bag can still be your carry-on as long as it meets the airline's size requirements. The usual dimensions for domestic hand luggage are 22 x 14 x 9 in (56 x 36 x 23 cm). Some airlines will have a limit of 20 x 12 x 5.75 in (51 x 31 x 15 cm).