The most important thing you should provide with your re-usable bundles is unit tests set. Lately I solved two major cases which Symfony2 hasn't got out of the box: testing services, defined in Dependency Injection Container and running model tests with fixtures in fully isolated environment.

He includes code snippets for both solutions - a BaseTestClass for working with dependency injection testing and a ModelTestCase class that, in the setUp(), loads in the required fixtures so the test can be completely isolated.