OEM Vespa Rear Carrier Kit for Vespa 946 -1B000008
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 a chrome rear carrier to your 946 to allow you to carry all manner of things.
Installation instructions can be found at this .pdf link