I'm sure you already know this but... You should NEVER allow the spectator to see you extract the coin from the mouth of the bottle. This will give them the correct impression of how the coin got in there in the first place. As illusionists we should never give them the CORRECT impression.
I rattle the coin in the bottle and turn it upside down, one hand around the mouth of the bottle, remarking how it's impossible to remove the coin. "No matter how hard you shake it." A coulple quick thrusts toward you waiting hand and the coin slides out. I use the original coin behind the bottle so show the coin still in there and squeeze it out the bottom.
Check out Oz Perlman's performance in Half Bottled