Credit: Maggie Slepian / Travel + Leisure As a frequent traveler and travel writer, I constantly test new packing systems for road trips and airline travel. Once in a while, a personal item or carry-on backpack hits the nail on the head. This year, it’s the Baggallini Tribeca Expandable Laptop Backpack—on sale now for up to 37 percent off. This tidy, structured backpack has already been with me on flights all over the country, fitting perfectly under airplane seats and rarely leaving my side throughout my trip. When I’m not traveling, this structured backpack stays packed and organized with my laptop, planner, work headphones, and a few snacks and necessities. The two elastic-topped side pockets hold my travel mug and water bottle securely in place, and the plethora of pockets makes organization a breeze. This is one of the most convenient backpacks I’ve ever tested, and it has become my go-to as both a commuter bag and a personal item during air travel.…