Gnome 3: Add a Custom Item to Favorites

Install and run alacarte. This tool allows you to manage the applications you see in the window Activities --> Applications. Those shown there are a subset of the ones available.

1. Create a new one in Alacarte with New Item in an existing or new menu.
2. Check the Show checkbox.
3. Go to Activities --> Applications and right click on the icon to add to the Favorites side bar.