I made up a game for the practice green I called 7's. I would have 3 balls, pick a hole and try to get all 3 up and down in 7 or less. I wouldn't leave till I had done it. At first it would take nearly an hour. I started getting pretty good at this game and got to the point I could do it 9 times out of 10. That's when I changed the name to 5's.
It's good for a little pressure putting too. When you are on your 8th hole and need to drop a 3 1/2 footer to go home, that's good for the mental game.