You will find most of the out of the box columns and content types on the file system of your local server:
For Site Columns look at:
- SharePoint 2010: HIVE14\Templates\Features\fields\fieldwss*.xml
- SharePoint 2013: HIVE15\Templates\Features\fields\fieldwss*.xml
For Site Content Types take a look:
- SharePoint 2010 HIVE14\Templates\Features\ctypes\
- SharePoint 2013 HIVE15\Templates\Features\ctypes\
What is not in the xml files stored in the directories is other content types then the one that exist in the SharePoint Foundation. Additional content types come with additional features and can be found the features folder there.
For custom columns you will only find this using SharePoint Manager.
Remember you can take a look into those files but you are note allowed to change this files. Handle with care.