This gist shows you how to easily create a cassandra image with initial keyspace and values populated.
It is very generic: the entrypoint.sh is able to execute any cql file located in /docker-entrypoint-initdb.d/,
a bit like what you do to initialize a MySQL container.
You can add any *.sh or *.cql scripts inside /docker-entrypoint-initdb.d, but note that:
*.shfiles will be executed BEFORE launching cassandra