Automatically install missing packages with package.el

gistfile1.el

;; ~/.emacs.d/package.el from http://repo.or.cz/w/emacs.git/blob_plain/1a0a666f941c99882093d7bd08ced15033bc3f0c:/lisp/emacs-lisp/package.el
(when
    (load
     (expand-file-name "~/.emacs.d/elpa/package.el"))
  (setq package-archives '(("ELPA" . "http://tromey.com/elpa/") 
			   ("gnu" . "http://elpa.gnu.org/packages/")
			   ("marmalade" . "http://marmalade-repo.org/packages/")))
  (package-initialize))

(setq mypackages '(clojure-mode slime slime-repl magit auctex))
;; Make sure that all packages from mypackages are installed
(dolist (p mypackages)
  (when (not (assoc p package-alist))
    (package-install p)))