The designer Idan Yosefov can appreciate the value of a functional and versatile bag. The 29-year-old Israeli traveled the world for five years before completing his master studies in leather-bag making in Florence, Italy. Last year, following a journey that took him to Cambodia, Australia, the Netherlands, and Los Angeles, he cofounded Martella Leather Bags (martellabags.com). The company, which makes its products in Istanbul, offers 10 models, including the $810 Due Terzi (“two thirds”) shown here. It can be carried as a briefcase or a backpack, and it includes a protective smartphone compartment.