Rear Carrier Kit for Vespa 946, RED - 606602M
Despite all it's beauty, the Vespa 946 is woefully ill suited for storage of anything larger than a cell phone. The good news is that with this official Vespa Accessory, you can add RED Rear Bag 606528M (no longer available) to your 946 to allow you to carry all manner of things.
Installation instructions can be found at this .pdf link