I would like to use org-mode's contributed packages: http://orgmode.org/worg/org-contrib/
[EDIT] SOLUTION:
As per answer below: 1) First one should have the elpa packages added.
(require 'package)
...
(add-to-list 'package-archives '("org" . "http://orgmode.org/elpa/") t)
...
(package-initialize)
This is described [here] in detail.1
2) Afterwards, below the lines above, one can add the desired modules like this:
(require 'org-checklist)
WARNING
Some packages may be available in the git-hub repository but not yet in the official repository. (e.g org-eww at the time of writing).
As such, requiring these will cause errors.
Before adding a requirement, it is reccomended to browse the folder:
~/.emacs.d/elpa/org-plus-contrib-<DATE>