Really interesting. I was born in 73 but can remember quite a bit from that pre-school to end of infants period. Outside loos at one playgroup, strikes, power cuts and candles. Anyway, food. My recollection will reflect households with young DCs of course.
While I agree there wasn't snacking in the sense of grazing, there were Elevenses and Supper - in the late evening snack, following an early tea sense. So that's five meals / substantial snacks in a day, for some I'd guess many people.
I guess Elevenses were an 'at home' thing, perhaps enjoyed most by children and pensioners but I bet far more workplaces had proper tea breaks morning and afternoon than now, and that tea came with biscuits. I remember there being a lot of biscuits. Everyone had biscuit tins - so a steady supply, not the occasional packet, mostly for guests, I buy now. I have young DC, don't offer biscuits often. I had 'biscuit time' daily as a pre-schooler at home (Elevenses) and we always had a snack of biscuits and squash at playgroup.
We did eat an amount of processed food - fish fingers, baked beans, tinned hotdogs were a fave (yeuch), Angel Delight and I remember the Fray Bentos pie.
Alcohol use varied by social class I think and massively by gender. Ladies did not go to pubs. But upper-MC families had wine with dinner. In the 70s there was a huge explosion in home brewing and wine-making, I remember my dad doing this. Part of the economic downturn, a huge fashion for everyone making all sorts of things.
Also, there was a bread strike, so all the SAHMs baked bread for a while. Some continued.
In my family and their MC section of society, there was definitely a social expectation of slimness. It was a social duty. Being overweight would have been seen as a moral failing, slatternliness. That came from my grandparents' generation but I felt it from them, and a bit via my mother, as a teen in the 80s.