Well... It's actually a fairly deep question. The "Distraction Free Writing" proponents seem to actively oppose providing buttons, but they do support keyboard shortcuts (click the ? for help). And there are also suggestions to rearrange your edit panel (moving pieces below the edit window, minimizing the navigation sidebar) to make the "normal" window more like "full-screen".
On the other hand,
Hover over the full screen edit button and you'll see a tool-tip - ALT-Shift-G
Typing "Alt-Shift-G" (in 3.4.1 for me sometimes) gives me a "full-screen" editor with the full complement of editing buttons -- *not* the Distraction Free Writing version, but the "old style" full-screen mode.
I'm not sure this works reliably and I don't think there's any inclination to improve support of it in the future.
FWIW, there's an "idea" opened for this at
http://wordpress.org/extend/ideas/topic/combine-distraction-free-writing-and-kitchen-sink#post-22608 with a link to a discussion in the support forums and a trac ticket, but the idea itself has been marked as "pluggable".