I get "I need xyz", to which I reply "I need you to use your manners", which usually works. It can just as easily result in a tanty though lol.

With the inappropriate food, we have introduced the concepts of healthy food and sometimes foods, so if he asks for a biscuit at breakfast time, I will tell him that it a sometimes food and we need to have a healthy food for breakfast to give us energy etc. Seems to be working (for now...), he is even asking for "a drink of water please, because it is the healthy choice". It sort of softens the blow of not getting junk food when he wants it if there is a reason.