As Martijn also writes, the quickinstaller takes care of this and it's merely a simple declaration of a dependency you can do in your package, to have the product installed on site-creation automagically, which takes two simple steps:
In the your.package/setup.py add:
setup( ...
install_requires=[ ...
'collective.blog.star'
To let buildout know, this egg shall be pulled and be provided to the ZOPE-instance, too.
And in your.package/your/package/profiles/default/metadata.xml add:
<object ... >
<dependencies>
<dependency>profile:collective.blog.star:default<dependency>
<dependencies>
To actually activate the dependency-product, when you install your product, via profiles.
Check if the profile's name is really 'default' as this is just a convention, defined in the configure.zcml of the product.
It might be, that the order of install can be crucial, as you also want to create content in the same process, I don't know by heart which step would be executed first, the c.b.star-install or the content-creation, you have to test this. In case, the order isn't right, you'd probably have to write another package for splitting the two tasks, controlling the order of install according to the position in the eggs-definitions-list (first comes first, IIRC).