You can choose what commands are displayed in the quick access toolbar. Take into account that some of the commands you wish to add to the quick access toolbar may only be available in certain contexts.
To access the options for customizing the quick access toolbar, go to the View tab > Ribbon Customization > Quick Access Toolbar > Quick Access Toolbar.
To reset the Quick Access Toolbar to show only the default commands you will also have to reset all tabs you customized on the ribbon to their default state.
To reset the ribbon to default, click Reset in the Customize Ribbon window.