After over 7 months traveling and putting this list to the test, I’ve also updated it and shared some thoughts on what I would do differently.
I chose the Osprey Farpoint 55 with a zip off day pack. Before we left, Nate and I used the day pack regularly and it was the perfect size for taking to baseball games, picnics, or day trips. The backpack itself is a good size for a carry-on and there is a cover for the straps that make it easy to store. It is bigger than is absolutely necessary but I am also taking more things than is absolutely necessary, so it all works out. When fully packed with the daypack attached my bag weighed between 20-25 lbs. With the hip belt on, it was comfortable and not tough on my shoulders.