Pull packages from repository. Requires melpa and marmalade, unless you change the packages in the list.

.emacs.el

;; check if the packages are installed; if not, install it.
(mapc
 (lambda (package)
   (or (package-installed-p package)
       (if (y-or-n-p (format "Package %s is missing. Install it? " package))
           (package-install package))))
 ;; The list of packages that should be installed
 '(yaml-mode wrap-region autopair color-theme-sanityinc-tomorrow creole-mode crosshairs
             col-highlight elpy auto-complete ac-js2 elscreen expand-region gist
             find-file-in-project flymake flymake-cursor fuzzy gitignore-mode
             highlight-indentation hl-line+ ido-ubiquitous idomenu iedit js2-mode
             js2-refactor dash magit git-rebase-mode git-commit-mode mark-multiple markdown-mode
             maxframe minimap multiple-cursors nose pony-mode popup s shimbun skewer-mode
             simple-httpd smex solarized-theme typing unbound undo-tree virtualenv vline w3m
             yasnippet zenburn-theme powerline unicode-fonts json-mode feature-mode web-mode))