I leave the country before it expires and I don't plan to renew it as my contract/project engagement in China has ended and there are no immediate plans to return after my Z visa expires.

Am I supposed to hand the small books over to someone? Customs/Immigration at the airport?

no one?

no. you dont have to hand them to anyone. so keep them for interest sake or cut them in half after leaving the country and throw them away. simple.

thanks for that!