Cassie, it might sound crazy but try to catch him being good. Even if he only does the right thing for 5 seconds jump in and praise him. If he's throwing food on the floor then the second you see hm putting some in his mouth tell him what a good boy he is for eating his food (usually I don't think that eating should be praised but if the opposite behaviour is driving you nuts I'd say go for it). Once he gets a taste for praise you might find that it gets easier to catch him doing the right thing.
Also try and reduce his capacity to say no - move some things out of his reach and instead of saying 'no, don' touch that' try distraction techniques instead. When you see he's interested in something off limits say 'ooh look what I've just seen. Do you want to try and see what it does' and offer an alternative.
Yasin and Imran are both into aeroplanes and helicopters and trains so sometimes when they start shouting I'll just say 'shhh, can you hear a helicopter, listen' and then I say I must have been mistaken. The distraction helps them to change direction.
Programs like PPP help you heaps with techniques like that and other ones.

Also what about family diet? Some children react far more to additives and so on than other children. maybe cutting colourings and sugar from his diet might help him.