I would bet that the majority of spending by nearly all people in the supermarket is discretionary spending.
It isn't the bread veg and meat that push the bill up for me, it's the alcohol, Sweet things etc, and that's ignoring all the stuff on the centre isles.
So I don't really agree with this statement at all
edit:
I am wrong, posted below, but I'll put it here too.
the uk spends £117.97 on food and non alcoholic drinks annually https://assets.publishing.service.gov.uk/government/uploads/...
£27 billion on alcohol consumption in the home https://www.statista.com/statistics/281935/spending-on-alcoh...
savory snacks seem to be around £3bn, sweets around £6bn, and the soft drink market around £10bn
So it doesn't really get close, no matter how you slice it.
total supermarket spend is £188bn
https://www.ibisworld.com/united-kingdom/market-size/superma...
So actual food still makes up the majority of sales, which im surprised by.