You never want something until you can't have it. So, each week in The Sell-Out, we're getting the scoop from your favorite retailers on what's selling like crazy. Watch this space to find out what everyone's buying, sign up for wait lists, and keep tabs on restocks.For sophisticated basics and workwear essentials, Modern Citizen has become our hidden gem of a one-stop shop. But we'll be the first to admit: We've kind of overlooked its accessories section. Until now, since they're actually some of the most popular (and best-selling) pieces.According to the company, its Rio Leather Crossbody bag sold out in just three days. Featuring an adjustable strap that can be worn crossbody or on the shoulder, a single open pocket on the inside, and a metallic clasp and loop closure at the front, this is pretty much the perfect everyday bag. And that versatility probably has to do with why it flew off the (virtual) shelves so quickly. A bonus? It's genuine leather and comes in at just $120.If you're as obsessed with this LBB (little black bag) as we are, you can pre-order it here to ship in about two weeks. Or, if you're in a hurry, you can shop some similar picks ahead. Ether way, consider your new go-to bag found.