Keep your back to the wall and your eye on the door.
While your at it, keep your hand on your holster.
I eat with both hands....
;-)
However, I am always aware of my surroundings.
I might be a bit leary of serving coffee to anyone who couldn’t keep their hand off their holster. The restaurant people have no idea if you plan to use the weapon for harm or for good unless you are also wearing a uniform and a badge.