The Windows 8 AppBar comes with a set of default icons embedded in a set of AppBarButtonStyles.
These styles are available inside the StandardStyles xaml file inside the Common folder of your Windows 8 XAML project.
The strange this was that when I tried to apply these styles to my AppBar buttons, Visual Studio complained that it couldn’t find the related resource:
<Button Style="{StaticResource AddAppBarButtonStyle}" />
I spent way too much time before I discovered that for one reason or another the AppBarButtonStyles were commented out inside the StandardStyles.xaml. Doh!
After uncommenting the styles I wanted to use, it worked perfectly.