I don't know that people have to change their behavior all that much. They just have to use some sense. I'm probably dating myself, but when I was a kid, we drank sodas fairly often. Except they came in 8 oz. bottles, and I had to share one with 2 siblings. Now, they're in 20 oz. servings, and everyone has their own.
Donuts, muffins, cookies, etc. were much less than 1/2 the size of the ones we get today.
A hamburger was more likely to be 3 oz. than the 8-12 oz. ones we see today.
And so on.
More is not better, but there really isn't that much wrong with what people really want to do.
And I'd wager they were better tasting, too. Smaller quantities, higher quality.
Less.
McDonalds used (and still uses) 10 burgers per pound of meat. Ray Kroc said that he wanted to simplify inventory; 100 buns = 10 lb = $15 in sales.
After Dave Thomas (Wendy's) introduced the 1/4 lb patty as the "standard", McD had to counter with it's Quarter-pounder®