Have him try to peel a clementine or small orange. This will give him practice grasping something small with his fingers while pulling at the same time, a skill he's going to need for writing. (Plus, he's rewarded with a sweet treat when he's finished!)
Instead of tossing those broken crayons, let your child color with them. He'll have to hold the smaller pieces the way he would a pencil rather than with the closed-fist grip he uses on whole crayons.
Drop by drop
For some kitchen fun, give your child a medicine dropper from an empty bottle, a cup of water, and an empty cup. Have him transfer a drop of water from one cup to the other to build finger strength and coordination.