He would look more like he was enjoying it if he wasn't concerned about looking at the camera. I do like the fact that you made it obvious that he's at the beach. Good cropping.
The boy's lower lip bulging out over the rim of the can is really unappealing. It looks like his nose is jammed into the can. Next time, take a look at some actual soda ads and notice how they are posed.
The cropping is way too tight. I like the background.
Your subjects eyes are looking toward the photographer. That distracts a little bit... shows he is not really focusing on enjoying the drink. (Im looking from a purely advertising point of view)
Great shot. Good idea. Suggested improvement IMO -- dip the can in water to show more water drops on it (greater impression of refreshing), and try and have the models eye straight ahead, not looking at the camera. :-)