Missing "show package contents" cmd
Show Package Contents is not for showing the contents of .pkg files, it's for showing the hidden structure for Applications (and other bundles), which are actually folders. You can use the program Pacifist to look at the contents of .pkg files.

To answer the question in your comment, here's how you can tell in Terminal. When you perform an ls -l command, directories have d as the first character in the line.

516 $ ls -l
drwxr-xr-x    3 steve  admin         102 Jan  6  2011 Form Viewer.app
drwxrwxrwx@   3 root   admin         102 Jan 18  2010 FormViewerFonts.pkg
-rw-r--r--@   1 steve  staff  2157020198 Jun 30  2012 MacTeX-2012.pkg


In this example, the first two entries are bundles and the last isn't.