You need the same basic accessories like any other saxophone. A good mouthpiece and reed are crucial when it comes to making a sound on the subcontrabass sax, but there aren't specific accessories for the instrument. Using a baritone saxophone mouthpiece can fit, which is why playing the bari sax a lot can help you prepare for the switch. You can pair it with a baritone sax reed or a reed for the bass saxophone or even the contrabass clarinet. Another beneficial accessory to have is a stand for the saxophone itself. That way, you can easily take a break without having to lay it down, but the stand can keep it upright while you play.