S.M.
Make him say please (nicely) before he gets anything. I get down on my 3 year old's level and say "say please" and then demonstrate saying it in a pleasant tone. If he says please but with a whine, I demonstrate again. Usually he smiles soon and says it sans whine. Otherwise, I would walk away and try it again with the next request.
Signing would also be a great way to increase his confidence in talking.