D&D Beyond doing a digital advent calender.
I claimed mine this morning, and got 11 Monsters to use from the latest sourcebook Dragonlance.
The RRP/Money saved is debatable - Usually Source books cost $40 yank bucks or so, but there are sales, memberships etc that make it cheaper, plus you have the option of buying only the indiviudal items you want from source books for a gold coin.
At this point I don't know whether its the same gift for everyone or random but imagine Ill get confirmation through here shortly.
Edit: Seems you can go back and claim missed days - the next days gift was a voucher for a DnD Version of Trival Pursuit.
From the website below
Light the fireplace and prepare a cup of tea, because the 2022 holiday season is here—and we're bringing the gifts! Each day starting December 5th, you'll enjoy holiday cheer with this 20-day D&D advent calendar. (Also known as an adventure calendar.) To get started, click on the dice below!
Confirming for you that 11 Monsters and Trivial Pursuit were 5/6 for me as well.