It would be a start if the quality of fast food wasn't so poor.
DS1 absolutely insisted on lunch in MacDonalds a couple of years ago. Aside from the fact that I could have got several huge mumsnet threads out of the family sat behind us, it was a pretty dire experience. I ordered myself a filet o'fish (wtf?) "meal" A soggy, bland square fish finger thing in a sticky sweet bread roll with some excuse for lettuce sneezed onto it and some tasteless fries. DS2, a hardened beige food eater (ASD and huge sensory issues around food) wouldn't even touch my fries. By the time I'd eaten what I could, I felt bloated but still light headed, as if I'd had nothing to eat.
In contrast, I can make myself a fish finger sandwich at home, with some sort of wholegrain bread, lots of flavour (even with cheap birds eye pollack fish fingers) and lots of crunch, with fewer calories, more complex carbs and undoubtedly more protein (not to mention the huge pile of lettuce, if I have any) and I feel satisfied, afterwards.
My beige eater, despite his restricted tastes, undoubtedly eats a lot better than many people without his sensory difficulties do.
And this is where I admit that we're having cauliflower cheese with roast chicken, tonight. I made a big pan of it (not with cream, the stomach cramps would be unbearable), last night as the centrepiece of our meal and have some left over.