I have two:
The first is just a personal pride story. But, on holiday a few years ago, my family (husband, 7 year old & 9 year old) worked out that the Spot It! game (or Dobble in the UK) is actually almost a finite projective plane of order 7. The game needs 2 more cards to correlate exactly with PG(2,7). The kids then took the axioms for a finite projective, sorted through the 55 cards in the deck, and then correctly determined which symbols belonged on which of the two missing cards in order to have that bisection with PG(2,7). My daughter later that week created her own Spot it! game based on PG(2,2), so 7 cards, 7 symbols, 3 symbols per card and each symbol appeared on exactly 3 cards.
The second story is not related to my university job, but rather to outreach that I have done in several local elementary schools. Once a week, I have had the pleasure of going to an elementary classroom and introducing these students to various (albeit primitive) cryptographic techniques. We will discuss the origins or history of a cipher, learn how a message was encrypted, and then practice decrypting an already coded message. I really enjoy sharing the different cipher techniques with these students. I was thrilled when I showed up one day and found that the entire class (approx. 22 students) had encrypted me personal notes of thanks for working with them that year. It took me over a day to decrypt the messages, but I still have all of these letters! And 1.5 years after showing a class of 3rd graders some ciphering techniques, my daughter received an encoded letter in the mail. At the bottom was a postscript. It read, ‘I really enjoyed doing cryptography with your Mum.’