Add an external javascript/css file to Magento

<action method="addJs"><script>js/custom.js</script></action>
<action method="addCss"><stylesheet>css/custom.css</stylesheet></action>
OR
<action method="addItem"><type>skin_js</type><name>js/custom.js</name></action>
<action method="addItem"><type>skin_css</type><name>css/custom. css</name></action>