The following suggestion was sent in by a reader:
I have found this a helpful brain stimulation, and it is easy, most people have a computer, with games.
Play solitaire, and when you get dealt a card eg… red 7, you state in your mind as quickly as you can,, the card before must be a black 6 and the card after must be black 8. Force yourself to think quickly about these choices. It might sound silly, but it does make you think quickly