My design principle for my cabinet is : "I don't want to help".
As soon as a friend asks me "How do I...?", a part of me dies inside.
So having a dedicated Quit button was essential for me.
You can see from my control panel that I have the following dedicated buttons:
Escape (Which I should have called QUIT)
Next List
Previous List (This doesn't seem necessary anymore since I don't have very many lists)
Save Game
Load Game
Volume + (These are kinda optional, people don't seem to care about the volume much and lots of designs just use a knob sticking out somewhere or hidden somewhere)
Volume -
Pause

Some functionality I've added since I designed my control panel:
The Next List did nothing in MAME, so now it brings up the
Command ListThe Previous List also did nothing so now it brings up the
Cheat List. Although maybe cheating shouldn't be so accessible?

Joseph Elwell.