It's best if you don't!
Our system uses the tracking numbers for individual items to update the status of your returns. When multiple returns arrive in the same box under one tracking number, our system isn't able to update the status of the extra items from "authorized" to "delivered."
We also have multiple fulfillment locations and your label routes the return back to the correct warehouse. If you send multiple items back in one box, those items may be sent to the wrong warehouse.
When multiple returns are sent back in one box, the additional items will be significantly delayed in being processed.