This is one of those plugins that I will only upgrade to a new version of Moodle once I have verified that it still works!
Sharing cart allows teachers to easily share/copy activities between different courses. It is much faster than the duplicate feature (I have been told) and very user friendly. It adds an entry in the activity/resource edit menu that you click to Copy to Sharing Cart. The activity/resource then just jumps over to the Sharing Cart block and can then be added to any course from the block. You do need to add the block to each course that you want to use it in. Sometimes quizzes will be a little slow loading but it is much easier and quicker than going through the import or restore process.
The maintainers are awesome as well, and very quick to respond to any bug reports. If you want to make your teachers happy, install this plugin for them! I only wish that I could automatically load it on every course page for my teachers but it is built to be user specific and so each teacher does need to add it themselves.