<global>

  <helpers>
    <myclass>
      <class>Vendor_Module_Helper</class>
    </myclass>
  </helpers>

  <blocks>

   <myclass>
        <class>Vendor_Module_Block</class>
   </myclass>

    <catalog>
      <rewrite>
        <product_list>Vendor_Module_Block_Catalog_Product_List</product_list>
        <product_list_toolbar>Vendor_Module_Block_Catalog_Product_List_Toolbar</product_list_toolbar>
      </rewrite>
    </catalog>

     <catalogsearch>
      <rewrite>
        <layer>Vendor_Module_Block_CatalogSearch_Layer</layer>
      </rewrite>
    </catalogsearch>

  </blocks>

<models>

    <myclass>
          <class>Vendor_Module_Model</class>
  </myclass>

  <catalog_resource>
       <rewrite>
            <product_collection>Vendor_Module_Model_Catalog_Resource_Product_Collection</product_collection>
       </rewrite>
   </catalog_resource>
 </models>
 ....