Select the option to 'Copy Content From Another Course' from Manage Site --> Site Content --> Add/manage Your Course Content.
You will see a list of courses you have taught in the past. Select a course to view the files in that courses's directory and any links that may be associated with them. If you would like to view a file, click the file name.
You may only copy content from one site at a time. Once you have determined which site you would like to copy content from, check the boxes under the Copy File column next to the files that you would like copy. You can select to copy all of the files by checking the top box in the Copy File column. In addition to the actual files, you also have the option to copy over any associated links (e.g. if the file was linked off of the existing site's main menu--you will see the link name in the Linked As column. If the file was saved to the course directory but was not directly linked from the existing site's main menu--the Linked As column will be blank. Once you have made your selections, click the Copy Selected File and Links... button.
Important Note: if a file already exists with the same name in your course directory--it will be overwritten with the new file. You will receive the warning below with the option to continue or cancel.
Once the files/links have been copied over, you will see a message confirming the copy.
The links (if you opted to copy them) will be visible on your course's main menu. If you opted to just move files, the files will be saved to the course's directory and you can add links to them using the Manage Site-->Site Content controls.