How we pack a parcel so it arrives in one piece

Every December we post a few hundred parcels, and almost all of them arrive whole (sample note).
The gift is wrapped first, in the paper you chose, with its tag tucked flat under the twine. Then it goes into a box one size bigger, with crumpled paper on every side so nothing moves when you shake it.
Glass gets its own small box inside the big one. The outer box is plain, so nobody at the door can guess what is inside.