In order to do that, we have to give them editing rights, since the Copy to Sharing Cart option is an item in the editing dropdown:
However, that enables them to edit, delete, show & hide, and other actions, on those activities, which we don't want. We only want them to be see the Copy to Sharing Cart item:
We're willing to create a new role for that, but we can't find the correct permissions to give that role in order for that to happen.
Are we missing something? Is there a way to do this, or is permissions by editing item too granular ?