How to customize the 'node content links' block?
I was looking for this myself and come across this link:
http://makandracards.com/jan0sch/11463-drupal-organic-groups-extras-add-content-links

If you're using Drupal 7 and Organic Groups (2.x) you probably have the OG extras module enabled.

The documentation to enable the "create content" links for your organic group nodes is sparse. Therefore a short howto:


Enable all needed modules Enable the module entityreference
prepopulate! 
Go to "Structure" -> "Content types" and select your
group content type, not your group type. 
Click on "manage fields" and edit the field "og_group_ref". 
Enable the checkbox labeled "Enable Entity reference prepopulate". 
Enable the block named "Node content links". 
Now you should be done. Steps 4-5 are needed for every group
content type in case you have multiple content types that can be
posted to groups.