<extension version="2.5" type="plugin" group="your_custom_group_name">

<?xml version="1.0" encoding="utf-8"?>
<extension version="2.5" type="plugin" group="[Your Plugin Group Name]">
	<name>[Component Name] - [Plugin Name]</name>
	<author>[Your Name]</author>
	<creationDate>October, 2012</creationDate>
	<copyright>Copyright (C) 2011</copyright>
	<license>GNU General Public License version 2 or later</license>
	<authorEmail>me@mydomain.foo</authorEmail>
	<authorUrl>www.mydomain.foo</authorUrl>
	<version>1.0</version>
	<description>Description of plugin and it's purpose goes here</description>

	<files>
		<filename plugin="[Plugin Name]">[plugin_name].php</filename>
		<filename>index.html</filename>
	</files>

	<config />

</extension>

<?php
defined('_JEXEC') or die;

class plg[Plugingroupname][Pluginname] extends JPlugin //Replace group and plugin values in the Classname
{	
	//Invoke the plugin upon user login
	//This was onLoginUser in J1.5
	public function onUserLogin($user, $options) // parametise the function as required
	{

	// populate
	$field1 = $this->getOtherRelatedData($user);
	$username = $this->getOtherRelatedData($user);

	$myCustomSession = array();

	$myCustomSession['name_of_array'][] = array('value1' => $field1, 'username' => $username);
	$myCustomSession['other_data'][] = array('other_val1' => 98765, 'other_val2' => 'Some other information');

	$session->set('myCustomSession', $myCustomSession);
	
	return true;

	}

	// Get some data that you only want called from the plugin itself
	
	private function getRelatedData($user)
	{
		$db = JFactory::getDBO();

		$query = $db->getQuery(true);

		$query->select('field1');
		$query->from('#__mycomponent_table');
		$query->where('field1 = ' . $user);

		$db->setQuery($query);
		return $db->loadResult();
	}

	// Get some data that you may want to call anywhere in your component - E.G. the user's username
	public function getSomeOtherRelatedData($user)
	{
		$db = JFactory::getDBO();

		$query = $db->getQuery(true);

		$query->select('username');
		$query->from('#__users');
		$query->where('id = ' . $user);

		$db->setQuery($query);
		return $db->loadResult();
	}
}