It can hold dozens of travel essentials and still feel lightweight.Credit: Travel + LeisureAs a travel writer who flies monthly (and sometimes more), I’ve become somewhat of a snob about my personal item. I try to fly exclusively with a carry-on backpack rather than a tote or purse to maximize packing space and avoid back pain while schlepping through the airport. But not just any backpack; something too big will take up precious leg space on my…