Possible Clues:

• Games played with a pack
• A hand might have five
• Eccentric characters offering greetings by post?
• Jacks and jokers, e.g
• Queens, kings and aces
• Perhaps Jack's getting marching orders?
• What's the big deal?
• Diamonds, maybe, found by detective sergeant beneath vehicle
• Pack of scoundrels surrounding king
• Chance pile, in Monopoly