Rob... love your avatar. He/she looks so sweet
I use leaves, pine cones and sand, all of which I have in abundance here. I add the sand last as the leaves and pine cones will break down. I have also put screen in first to cover the holes to keep the dirt from going right out of the holes. And sometimes if screen isn't handy I cover the holes with BIG leaves...keeps the dirt in long enough for the plant to get established