The Tom BIhn Pilot makes a great personal item for air travel. Ultra minimalists might even be able to use it as their only bag. Capacity= 13 liters. When not traveling, I use this for my EDC when I’m not in a backpack mood. Be sure to check out my reviews of the Tom Bihn Synapse 19, Osprey Porter 30, Osprey Porter 46, and Tortuga v2 backpacks.
More details on how I packed this for a recent flight: https://thesoulinspiration.com/2017/01/21/tom-bihn-pilot-as-a-powerful-personal-item-for-winter-travel/