Finger or hand puppets
Let him draw on his cast
A torch and some cardboard cutouts to make shadow puppets
A felt board and shapes to make up stories. You can buy them for around $14 at most toy shops and some news agents. Or you could make your own.
Stories to listen to.
Get some bright colorful cheerful posters for the ceiling and change frequently

Poor little thing. Hope it was an uncomplicated break and he heals quickly.