I'm going to disagree, if politicians are harping on about the cost of living (and pretending they can fix it) then they should know what those costs are.
Fairly much all the shops deny it but here in NZ there is definitely a Xmas tax, when the price of common staples goes up dramatically for a few weeks before Xmas. When Kumara that are normally $6/kg suddenly more than double in price, same thing with potatoes and pumpkin.
So yes, when you go shopping you get what you need but there is a point when I'll forgo certain items for others as we refuse to pay the rip off prices.
Something I've noticed here in NZ (as have a lot of other shoppers), bread is no longer delivered daily, rather they bring in big lots and it's stored in the chillers out the back. Bread that has been in a chiller tends to go off and mould very quickly, a quick squeeze test will tell you if it's fresh but it also pays to check the tag dates. Most times it's obvious if it's been in the chiller and I won't buy it.
For some items there are definitely price cycles, so buy and stock up when cheap so you don't have to buy when it's expensive. I see no reason to give those rip off supermarkets and more money than absolutely necessary.
We also go to the local markets on the weekend, quite often they have as good or better fresh produce at better prices and at least the money is going to the growers instead of supermarket shareholders pockets.
I certainly don't know what most of the regular prices are in the shop but no doubt the missus does, I'm just the trolley boy and the long arms to reach items she can't get.