We don't have a specific box but everyone in the house does get a new pair of pyjamas (current favourite characters usually, never Xmas ones), a new book and a new toothbrush, a gift bag magically appears at the door after I have sent a text to my neighbour saying the coast is clear
There are different suspicions as to how they get there, but I have never been a suspect because I get stuff too! Top on the list are elves, fairies, father Christmas and nanny
It's just following on the tradition from my childhood. My DM said that the main aim was to get the 3 of us to bed at a decent time despite the excitement, so we would brush our teeth (mainly the toothbrush was because my older sister put up a fight most nights about this and with a new toothbrush she wouldn't) put new pyjamas on and have stories in bed then go to sleep.
She also said that it was so that we all had nice pyjamas on for christmas morning photos, which was more important then because of the price of film and developing the photos, you didn't take as many through the year and you couldn't just delete the rubbish ones. Also so that she had the three of us in something new and clean, as there was a lot of hand-me-downs and being kids meant between us usually one would be dirty!
I loved the tradition growing up so it was something I always wanted to carry on. Anyone staying here on Christmas Eve will always get pyjamas, book and toothbrush, no matter who they are or how old they are. Although I am included, my DM still insists on buying mine and will put them in a bag and I'm not allowed to peek until Christmas eve when they are swapped in to the gift bag 