i assume you already found this function at the bottom of Store Settings under database management.  Just click on the 'delete all products and orders'.

The one thing it doesn't do is delete the entries from the Cat_advcatproducts table.  Those have to be delete manually.  Of course, since the products no longer exist, the orphaned records don't really hurt much unless you do this a lot and end up with a large index during advanced category searches.