The Surface Duo 2 Pen Cover is not cheap, but it's the best accessory even if you don't use the pen.

There aren't many accessories for Microsoft's Surface Duo 2, partially due to the complexity of creating cases and even screen protectors (the new inward curving displays are tricky). But Microsoft did show off the Pen Cover back when the Surface Duo 2 was announced in October, which looked intriguing.