We do our best to limit junkfood and candy in our house. It isn't restricted but it's also not unlimited. None of us drink pop on a regular basis. I am the only one who will have a coke to top off a good and hearty cholesterol filled junkfood meal like pizza or fastfood. If I go halfway, I may as well go the distance.
We told them that if they say no to any of those types of items, we would do something nice for them whether it is go to the dollar store or take them somewhere special if they tell us that they refused to have those things. We have also told them that they can make us the bad guys if a situation becomes uncomfortable for them to say no.
On the flip side...
We are realizing that teaching them how to say no to these things at an early age is teaching them how to say no to other things later. If they are offered beer or drugs at a party, there is a strong possibility that they will say no if they feels it is not right to do. We are trying to empower them at an early age. All we can do is give them the tools to say no.
Obvously, it isn't a guarantee. We can only teach them what we can and hope it sinks in.
The most important key is being present and loving them more than anyone else can so they know home and family is the safest place for them to be themselves.