I assume you are talking about the flyout toolbar button. Flyouts do not show commands that are currently disabled (grayed out) so if you see that it is grayed out in the menu, then it won't appear in the flyout. Both Center of Mass and Mate Reference require some sort of geometry to be in the model, so as soon as you create a solid, then those commands will be available in the flyout toolbar.
The Grid System command is not on the toolbar by default. The commands that are present on this type of flyout is dictated by the definition of the standalone toolbar. So, to customize the toolbar, go to Tools, Customize and on the Toolbars tab, turn on the Reference Geometry toolbar (it should show up on the left of the screen). Then go to the Commands tab and select Features. Then drag the Grid System icon onto the Reference Geometry toolbar. Then go back to the Toolbars tab and turn off the Reference Geometry toolbar and exit the Customize dialog. Now the Grid System icon should be present on the Reference Geometry flyout.
For an overview of flyout tool buttons and their customization, see this blog post:
I hope this helps,