The good news is that your pup is young, and you should be able to resolve this while he is still small, and easier to handle than say, at a year old. I would also suggest puppy and obedience classes to socialize and establish your dominence.
Along with your firm "No", I would give the "drop it" command and grasp his muzzle firmly, holding it closed, and give it a firm squeeze while picking up the item with the other hand. Hold it out of his reach and make him sit, then give it back. Once he learns the "drop it" command, you should be able to not grab him, and take things away. Being able to do this is not just a matter of your safety, but his too, as puppies will get into things that can hurt them, and you need to be able to take that irresistible chunk of baker's chocolate (or whatever) from him withut losing a finger.
At mealtimes, enlist a friend. Put the food down, and walk away. Come back and say "back off", firmly. At the same time have the partner grasp collar or scruff, and guide the dog away from the bowl and press on hindquarters. When the dog sits, toss a couple pieces of highly prized treat (hot dog slices are great) in the bowl. Say "go see" and partner releases dog. They learn quite quickly that Back off is a positive command, and if they obey, they get something better than what they already have, and the partner is unneeded. I will still sometimes keep back a little something at mealtime occaisionally and add it in this manner. I just get the "ba..." out of my mouth and three butts, in three separate areas of the kitchen hit the floor, and they drool in anticipation waiting their turn.
Every male doberman, and my current dane/wolfhound puppy have challanged someone in the house over food/treats at some point , and we now can literally reach in their mouths safely to retrieve forbidden items. Good luck, and let us know how it goes for you.
Stella