My carry on is a Kelty Redwing backpack; I have been using it for the past 5+ years. I can get 2-3 changes of clothes in there, plus personal care and convenience items. It fits in the overhead and allows me to bring what I need for several days, if my check-in luggage gets delayed or lost. I can wear it and still have my hands free. While in county it serves as my primary piece of luggage, refilling it with clothing, etc. from the check-in luggage as needed.

Pete