eyali: That is correct, an empty GameObject.
Create the main panel as normal.
Create a new (empty) GameObject
Create 3 buttons, as children to that new GameObject.
In the Project window of Unity, create a new prefab and drag the new GameObject with those 3 attached buttons into the new prefab instance.
Then if you have different scenes with their own panels, you can still instantiate the prefab you've just created and get the same button layout everywhere (good for consistency across screens, which players like).