My kids went on a 2-week trip to Europe with EF Tours in high school, and one of the caveats was they had to pack in a single carry-on suitcase. No checked luggage allowed. There was an hour-long seminar on how to pack leading up to the trip. One of our big takeaways was the 35L Cotopaxi Allpa backpack is absolutely awesome for carry-on travel. At this point, everyone in the family has one. All of our other luggage is gathering dust in the basement as those backpacks are all we use anymore. I've also noticed if you are flying in the cheap seats on the plane and they are making the last boarders with carry-on luggage check their bag at the gate, they tend to only grab people with the wheeled suitcases, not the backpacks.