But those things EXIST in the world, and it is true that if you forbid them, they will become attractive.
I AM a bit of a freak about food, I make as much as possible from scratch, and I do keep healthy options around the house for DCs to choose. However, I also allow them to have sweeties occasionally, they love sausages (once and a while), and they have had crisps at parties and family gatherings.
As a result, they normally CHOOSE fruit if it's available, and they will CHOOSE cut up veg, as well...because I don't have a fit about what they eat, and I am relaxed when we're out, and I'm not the one cooking or providing the snacks. ONE DAY of eating a few things isn't going to do ANYONE a disservice...As long as he eats well the majority of the time, and gets lots of exercise, this won't affect him at all.
Really...you aren't going to be able to control his eating forever, and it shouldn't be about control...it should be about modelling and guiding healthy food choices most of the time, but also modelling that food is a lovely part of life, and a few crisps at a party is a nice treat.