That's pretty unusual. You mean you go into grocery stores and choose random products? Maybe you blindfold yourself, so that you don't know what you'll be eating until you get home?
My purchases are not usual. I have a large garden that I freeze/can. But depending on work I sometimes have very little time in the harvest season. So, some years I need to buy vegetables, other years I do not buy many at all.
I have friends with farms. So, I buy most of my meat from them when they have a spare 4H lamb that no one wants. Some years I don't need to buy any meat at all, other years I fill my freezer full.
I shop based on need/location rather than price. One store has great bread, so when I need bread, I do all my shopping at that store. Another has great bulk supplies. Another is located in a diverse section of town with better ethnic supplies. And a fourth is close to home. So, depending on my most pressing need (which is fairly random at the moment), I may go to any one of those 4 grocery stores. And each store has pretty drastically different pricing.
I'm not the typical shopper that buys the same things at the same store over and over again. When I do shop, the laundry detergent + wine bottles may be far higher in price than the salt/tortillas end up being. So, I just don't really notice the grocery price swings that much.