If you parked in a space where the meter still had time remaining on it you would consider it your lucky day and not give it another thought right?
I would be willing to bet that anyone who plays slot machines has, at one time or another, sat at a machine that either had a credit left on it or had a coin/token in the tray.
If playing that credit/sticking the coin in your pocket will cause you to loose sleep, don't do it. I, personally, do not see where playing/pocketing the credit/coin is grounds for the morality police to come knocking on your door.