I suggest you buy a hollow rubber ball about the size of a tennis ball. You can squeeze it using all fingers or one finger or any combination. So if your stuck in traffic or watching a movie you can just sit a squish the ball working your fingers. You can also change the angle of your fingers on the ball as you squish it building strength in different ways
I say hollow because for example. You can squish the ball with your 3rd finger, then squeeze hard enough with your first finger to push your 3rd finger up. Then use your 2nd finger to squeeze hard enough to push fingers 1 and 3 up, then use 1 and 3 to push 2 up. Make up combination along those lines. It will strengthen your fingers and help your mind get use to moving them in different combinations.
Kids toy section at stores or pet stores should be a good source.
