You can add everything that you can add to the Materials section, with the addition of Course Partitions. This includes, but isn't limited to:
Microsoft files (PowerPoint, Word, Excel, etc)
Images (JPG, PNG, GIF, etc)
Videos (MP4, AVI, FLV, etc)
YouTube/Vimeo videos
Rich HTML documents
SCORM 1.2 and SCORM 2004 packages
Audio (MP3, WAV, WMA, etc)
Assessments
Links