A simple Coin with a hole for a 10x3mm magnet and a 40mm diameter sticker I use for my Toniebox.
I used the following components:

• NXP RFID Tag (Original NXP ICODE SLIX-L)
• AVERY Zweckform Runde Etiketten L3415 (40mm diameter)
• 10x3 mm Round Magnets

How to use it:

1. print the 2 parts
2. insert the magnet in the hole of the thicker part (base) - make sure to check the correct orientation.
3. stick the NXP RFID Tag onto the base, covering the magnet and holding it in place
4. push in the thinner part (lid) into the base, locking it in place
5. print a 40mm Sticker and put it on the lid