A "must use" plugin to help save theme-agnostic functions

grd_functions.php

<?php
/**
 * Must-Use Functions
 * 
 * A class filled with functions that will never go away upon theme deactivation.
 * 
 * @package WordPress
 * @subpackage GRD
 */
class GRD_Functions {


	public function __construct() {

		add_action( 'after_setup_theme', array( $this, 'define_constants' ), 1 );
		add_action( 'init', array( $this, 'add_post_type' ) );
		add_action( 'init', array( $this, 'add_taxonomy' ) );
		add_action( 'wp_head', array( $this, 'print_header_scripts' ), 997 );
		add_action( 'wp_head', array( $this, 'enqueue_scripts' ), 998 );
		add_action( 'wp_footer', array( $this, 'print_footer_scripts' ), 999 );

	}


	public function define_constants() {

		// Path to the child theme directory
		$this->maybe_override_contant( 'GRD_DIR', get_stylesheet_directory_uri() );
		$GRD_DIR = trailingslashit( GRD_DIR );

		// Path to the css directory
		$this->maybe_override_contant( 'GRD_CSS', $GRD_DIR . 'css' );

		// Path to the images directory
		$this->maybe_override_contant( 'GRD_IMG', $GRD_DIR . 'images' );

		// Path to the included files directory
		$this->maybe_override_contant( 'GRD_INC', $GRD_DIR . 'inc' );

		// Path to the javascript directory
		$this->maybe_override_contant( 'GRD_JS', $GRD_DIR . 'js' );

		// Path to the sass directory
		$this->maybe_override_contant( 'GRD_SASS', $GRD_DIR . 'sass' );

		// Path to CDN
		$this->maybe_override_contant( 'GRD_CDN', 'http://cdn.gregrickaby.com/' );
		$GRD_CDN = trailingslashit( GRD_CDN );

		// Path to CDN styles
		$this->maybe_override_contant( 'GRD_CDN_CSS', $GRD_CDN . 'css' );

		// Path to CDN images
		$this->maybe_override_contant( 'GRD_CDN_IMG', $GRD_CDN . 'images' );

		// Path to CDN scripts
		$this->maybe_override_contant( 'GRD_CDN_JS', $GRD_CDN . 'js' );

	}


	public function maybe_override_contant( $constant, $value ) {
		
		if ( ! defined( $constant ) ) {
			define( $constant, $value ); // Constants can be overidden via wp-config.php
		}

	}


	public function enqueue_scripts() {

		wp_enqueue_script( 'some-script', GRD_JS . '/some-script.js', null, null, true );

	}


	public function add_post_type() {

		$this->setup_post_type( array( 'Code', 'Code', 'code', 'code' ), array( 'menu_position' => '1' ) );
		$this->setup_post_type( array( 'Gif', 'Gifs', 'gifs', 'gifs' ), array( 'menu_position' => '2' ) );
		$this->setup_post_type( array( 'Photo', 'Photos', 'photos', 'photos' ), array( 'menu_position' => '3' ) );
		$this->setup_post_type( array( 'Recipe', 'Recipes', 'recipes', 'recipies' ), array( 'menu_position' => '4' ) );

	}

		public function setup_post_type( $type, $args = array() ) {

			if ( is_array( $type ) ) {
				$types = isset( $type[1] ) ? $type[1] : $type . 's';
				$key = isset( $type[2] ) ? $type[2] : strtolower( str_ireplace( ' ', '_', $type[1] ) );
				$slug = isset( $type[3] ) ? $type[3] : str_ireplace( '_', '-', $key );
				$type = $type[1];
			} else {
				$types = $type . 's';
				$key = strtolower( str_ireplace( ' ', '_', $type ) );
				$slug = str_ireplace( '_', '-', $key );
			}

			$labels = array(
				'name'                => $type,
				'singular_name'       => $type,
				'add_new'             => 'Add New',
				'add_new_item'        => 'Add New ' . $type,
				'edit_item'           => 'Edit ' . $type,
				'new_item'            => 'New ' . $type,
				'view_item'           => 'View ' . $type,
				'search_items'        => 'Search ' . $types,
				'not_found'           => 'No ' . $types . ' found',
				'not_found_in_trash'  => 'No ' . $types . ' found in Trash',
				'parent_item_colon'   => '',
				'menu_name'           => $types
			);

			$rewrite = array(
				'slug'                => $slug,
				'with_front'          => true,
				'pages'               => true,
				'feeds'               => true,
			);

			$args = wp_parse_args( $args, array(
				'labels'              => $labels,
				'public'              => true,
				'publicly_queryable'  => true,
				'show_ui'             => true,
				'query_var'           => true,
				'rewrite'             => $rewrite,
				'capability_type'     => 'post',
				'hierarchical'        => false,
				'menu_position'       => '5',
				'has_archive'         => true,
				'exclude_from_search' => false,
				'supports'            => array( 'title', 'editor', 'excerpt', 'thumbnail', 'genesis-cpt-archives-settings' ),
				'taxonomies'          => array()
			));

			register_post_type( $key, $args );

		}



	public function add_taxonomy() {

		$this->setup_taxonomy( 'Tag', 'Code Tags', 'code', 'code-tags', array( 'code' ) );
		$this->setup_taxonomy( 'Tag', 'Gif Tags', 'gifs', 'gif-tags', array( 'gifs' ) );
		$this->setup_taxonomy( 'Tag', 'Photo Tags', 'photos', 'photos-tags', array( 'photos' ) );
		$this->setup_taxonomy( 'Tag', 'Recipe Tags', 'recipes', 'recipes-tags', array( 'recipes' ) );

	}

		public function setup_taxonomy( $type, $types, $key, $url_slug, $post_type_keys ) {

			$labels = array(
				'name'                       => $types,
				'singular_name'              => $type,
				'search_items'               => 'Search ' . $types,
				'popular_items'              => 'Common ' . $types,
				'all_items'                  => 'All ' . $types,
				'parent_item'                => null,
				'parent_item_colon'          => null,
				'edit_item'                  => 'Edit ' . $type,
				'update_item'                => 'Update ' . $type,
				'add_new_item'               => 'Add New ' . $type,
				'new_item_name'              => 'New ' . $type . ' Name',
				'separate_items_with_commas' => 'Separate ' . $types . ' with commas',
				'add_or_remove_items'        => 'Add or remove ' . $types,
				'choose_from_most_used'      => 'Choose from the most used ' . $types
			);

			$rewrite = array(
				'slug'                       => $url_slug,
				'with_front'                 => true,
				'hierarchical'               => true,

			);

			$args = array(
				'labels'                     => $labels,
				'hierarchical'               => true,
				'public'                     => true,
				'show_ui'                    => true,
				'show_admin_column'          => true,
				'show_in_nav_menus'          => true,
				'show_tagcloud'              => true,
				'query_var'                  => true,
				'rewrite'                    => $rewrite
			);

			register_taxonomy( $key, $post_type_keys, $args );

		}

	public function print_header_scripts() { ?>

		<script>

			var _gaq = _gaq || [];
			_gaq.push(['_setAccount', 'UA-XXXXXXX-XX']);
			_gaq.push(['_trackPageview']);

			(function() {
			var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
			ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
			var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
			})();

	</script>

	<?php }


	public function print_footer_scripts() { ?>

		<script>
			// some javascript or jquery here
		</script>

	<?php }


} 

// Instantiate the class
$GRD_Functions = new GRD_Functions();

Gary Jones doesn't recommend the use of a Singleton: http://dsgnwrks.pro/development-principles/gary-jones-recommended-resources-on-avoiding-singletons/