I didn't understand the joke in my Christmas cracker, it read
"Help, I've been kidnapped & forced to work in a Cracker factory."
I don't see what's funny about that.

Last year it was better.
"What lies at the bottom of the sea, and shivers?"
"A nervous wreck."

Actually a cracker is one who cracks computer code for fun, but without using his abilities maliciously.
The malicious ones are called Hackers.