I have tried a lot of personal item bags over the years—backpacks, large totes, small totes and bags designed specifically to fit under an airplane seat. Some held far less than I expected, while others looked small but somehow fit everything I needed for a long flight. I became particularly serious about finding the right personal item after a Delta flight to Jacksonville. The plane was small, and passengers were required to gate-check their rolling carry-ons. Mine contained my laptop, medications and other things I wasn’t willing to check, so I had to stand at the gate hurriedly stuffing...