My observations (based on a 60's childhood and having parents who lived through rationing).
People didn't eat snacks. You might have a biscuit with your drink at 'elevenses' but that would be one biscuit, like a rich tea. Or an apple on the way home from school. You weren't allowed anything else, as it would 'spoil your tea'.
Crisps were an occasional thing, maybe one packet if you were lucky. A few sweets were a weekly treat and paid for out of your pocket money, they had to last until the next week.
Plates were smaller, they really were!
People didn't have as much disposable income, they would buy the minimum basic food and that was that - there would be just enough to go round. Plain cakes were made at home, and weren't laden with chocolate, cream or piles of icing like they are now. Shop-bought cakes were tiny - cupcakes were little things like a fairy cake with flat icing on the top, not piled high and bigger than the cake itself.
Nobody ate in the street, it was thought of as common and bad manners.
Fast food chains hadn't been invented, and going to a restaurant was a once or twice a year thing, and for a really special occasion. If you were out for the day, you would take a packed lunch. Maybe you'd have takeaway fish and chips on a Friday, but portions were far smaller than they are now - especially the chips.
Nobody was afraid to say "Don't be greedy, no you can't have any more, you'll get fat", or "No, you cant have that many sweets, they'll rot your teeth".
Kids played outdoors far more than they do now. I remember in the school holidays, we'd literally be out from morning to night, and only reappearing for a drink of water (sometimes with a tiny splash of squash in it) and for mealtimes, when we'd quickly eat so we could go out and play again. We'd burn off all the calories and everyone was as fit as a flea.
Very few people drank regularly at home. My parents only had alcohol at Christmas.