I am so jealous! Sorry, it's just that I have the opposite problem with my son! I have seen suggestions on this type of thing before. First, I wouldn't lock the fridge, but would make a special drawer or section of the fridge for him and his snacks. Of course you will only stock that drawer with things you'd want him to eat. I've heard this works well, because at this age, they will get locked into a power struggle with you over anything, because of their growing independence. Better to re-direct their behaviors rather than try to roadblock them, I think. And don't worry about not eating at meals. This is completely normal--toddlers and pre-schoolers graze, and this is actually a healthier way to eat. I don't care if my son grazes, as long as he is eating mostly healthy snacks. If we sit down to eat and he isn't humgry because he's snacked, he will either just eat a few bites, or I will serve him some fruit, which he will almost always eat. As for the juice, I would allow it--but just slowly change the ratio of juice and water until it is mostly water with just a splash or so of juice. As for the chocolate milk, that is up to you. Some moms are totally against it. I don't mind it, but I make my own, using Ovaltine or Carnation Instant Breakfast, so that I feel he is at least getting some additional nutrition out of it. If you do that, talk it up and call it his "special" milk. (I did this with my son when he wouldn't eat cheese--I bought string cheese and called it "special cheese" -- now he eats it up and asks for more special cheese!
BTW, here's where I got some of that info (having shelf space just for your toddler)...although the article is about picky eaters, it talks about typical toddler eating behavior, and also tips for feeding them...
http://askdrsears.com/html/3/T030800.asp
Good luck!