Plugin which runs a function to activate other plugins when new sites are created.

mdw-activation-plugin.php

<?php
/*
Plugin Name: Multisite Site Creation Activation Plugin
Plugin URI: 
Description: Plugin which runs a function to activate other plugins when new sites are created.
Version: 1.0
Author: Mark Wilkinson
Author URI: http://markwilkinson.me
License: GPLv2 or later
*/

/**************************************************************************
* Function mdw_plugin_actions_on_signup()
* Activate plugins on site creation depending on site type.
**************************************************************************/
function mdw_plugin_actions_on_signup( $blog_id, $user_id ) {
	
	/* get the site type from the user meta */
	$mdw_user_site_type = get_user_meta( $user_id, 'mdw_site_type', true );
	
	/* switch to the new blog that has been created */
	switch_to_blog( $blog_id );
	
		/* update this sites option for site type to the site type of the user */
		update_option( 'mdw_site_type', $mdw_user_site_type );
	
		/* get the site type option */
		$mdw_site_type = get_option( 'mdw_site_type' );
	
		/* get a list of the active plugins */
		$mdw_active_plugins = get_option( 'active_plugins' );
		
		/* create an array to store our plugins to activate in */
		$mdw_plugins_to_activate = array();
	
		/* switch depending on the site type */
		switch( $mdw_site_type ) {
		    
		    /* if this is a bronze site */
		    case 'bronze':
		    
		    	/* add plugins we want to activate to our array - in this case the bronze plugin */
		    	$mdw_plugins_to_activate[] = 'mdw-bronze/mdw-bronze.php';
		    		        
		        break;
		        
		    case 'silver':
		    
		        /* add plugins we want to activate to our array - in this case the silver plugin */
		    	$mdw_plugins_to_activate[] = 'mdw-silver/mdw-silver.php';
		    	
		        break;
		        
		} // end switch statement
		
		/* loop through each plugin we need to activate */
		foreach ( $mdw_plugins_to_activate as $mdw_plugin ) {
		
			/* check whether the plugin we want to activate is not already in the active list */
			if( ! in_array( $mdw_plugin, $mdw_active_plugins ) ) {
				
				/* no already active so lets push our plugins to activate into the active plugins array */
				array_push( $mdw_active_plugins, $mdw_plugin );
				
				/* update the option for active plugins to include our new plugins */
				update_option( 'active_plugins', $mdw_active_plugins );
				
			} // end if plugin not already active
			
		} // end loop through plugins
	
	/* restore the db context back to the original blog */
	restore_current_blog();
		
}

add_action( 'wpmu_new_blog', 'mdw_plugin_actions_on_signup', 10, 2 );

?>