"Give a shopping list plus price for a weeks worth of food for a family of 4, assuming no reliance on a 'store cupboard' and no meal sharing."
That's impossible though and not a fair comparison at all.
When you buy "junk" food, you eat it as you go and very rarely have anything left over.
When you cook from scratch you tend to build up a store cupboard as you go due to the fact you are using a variety of different ingredients to make it from fresh, dried and tinned. So if a recipe requires a certain ingredient, you would buy that, use it in your dish then keep it in the cupboard for the next use. You wouldn't throw it away.
So next time when a recipe needs certain things you go to your cupboard and use some of the things you have built up in there such as sauces, tins, dried goods etc. People who make from scratch don't throw the ingredients out after if they haven't used it all up so it is impossible to give examples of making from scratch but not allowed to go to the cupboard
and it's not about spending lots of money on cupboard staples, they are just things you gain over time when you cook certain foods.
Junk is just that, junk. You open it, shove it in the microwave or oven and your done and there is no ingredients to save for next time. Plus when you look at the salt content and nutritional value of some of that stuff, homemade meals are way better for you and your body.