My son takes his lunch to school everyday. He has his own little lunch carrier that helps keep the warm stuff warm, and the cool stuff... warm. Before long, he started putting his trash in his lunch bag rather than tossing it after he was done eating. To remind him that he needs to discard the used napkins, emptied ziplock bags, etc... I would throw in a little drawing in his bag that he would discover during lunch. He now looks forward to his little reminders, and so do I - they're fun to draw.
What began as a simple "toss your trash" message has evolved into fun single panel comic strips, sometimes with a running theme. Because these are drawn on 3x5 index cards, it's forced me to be conscience of what is important to telling a story...plus I typically have 2 minutes to crank them out.

He wore a Jawa costume for Halloween this year.


I drew Sir Elton because he played piano for his school's talent show.

Justin is because he played a Beiber song for the talent show.

This is one of his favorites because "it's so random."
Here's a link to some more.
http://weezl.blogspot.com/2011/12/lunch-cards-02.html http://weezl.blogspot.com/2011/12/lunch-cards-03.html