Our *tinyMCE card here on wagn.org has:

theme_advanced_buttons1 : "formatselect,bold,italic,"

The "formatselect" is what makes the menu appear in our edit toolbar, and the "bold" and "italic" puts the corresponding buttons there as well:

There's also a line with:

theme_advanced_blockformats : "p,h1,h2,pre",

...which is why the menu offers Paragraph, Heading 1, Heading 2, and Preformatted.