Here's an idea that might or might not work for you.

Don't label food as special or bad or good - its just food. Rather than having battles over it, have food that they can have free reign over. raw vegie sticks, fruit, sandwiches, yoghurt, water... whatever you are comfortable with and have. Involve them, work out if they can regulate for a week or just a day at a time. At first they might eat all the biscuits before breaky and then they have the choice of the other foods for the rest of the day.

i don't do time out, as in sit here for 4 minutes or whatever, but i do take DD to her room (generally when she hits DS) and ask her to sit and calm down and when she is ready come out and see if DS is ok. The door is open and she can come out whenever. for DD, making her sit somewhere just sets up a battle, and you have forgotten what started it and what you are trying to teach.

turning the tv off here helps everyone to be more productive, imaginative, active.

good luck