I grew up in a Catholic neighborhood in Pittsburgh and most of my friends went to St. Gabe's up on the hill so, although my family wasn't Catholic, I heard all the stories anyway. My favorite was the one about the little boy and the cookies.
The Little Boy and the Cookies
In preparation for First Communion, Sister X's second grade class was learning about the doctrine of the Real Presence: that Christ is literally, physically, present in the Eucharist.
Sweet, thought one little kid. After school one day he sneaked into church and knocked on the door of the tabernacle, the ritual cupboard on the altar in which the reserved eucharist is kept.
Hey, Jesus, he said, I brought you some cookies, and he laid out in front of the tabernacle the cookies that he'd saved from his lunch that day.
Preparing for mass next morning, Father Y found the cookies and, after (no doubt) puzzling a bit, ate them.
After school that day, the kid sneaked back into church. Pleased to see that his previous day's offering had been accepted, he once again knocked on the tabernacle door, and said: Hey Jesus, I brought you some more cookies. Once again he duly laid out that day's offering.
This went on for several days. Finally, one morning, the priest says, indignantly, Who's bringing all of these cookies?
(This line always got a laugh.)