The 40L backpack should be comfortable to wear for extended periods of time, but it's always good to try it on and adjust the straps[1]. Most 40L packs are about as large as you'll be able to bring onto the plane, but adding a few more liters is worth it if you can (and want to)[2]. The Osprey Farpoint 40 is a near-perfect backpack for beginner travelers and first-time bag buyers[3], with lightweight construction and back support, plus waist and chest straps to switch the weight to your hips[4].