I have a couple of brands that I am really loyal to, and then compensate with own brand or basic brands for many other things.
Biggest indulgence is De Cecco pasta. I just found supermarket own to be soggy and it sticks together and when we tried this brand we realised how much better it is - less gloopy, keeps its shape and texture however long you cook it (essential when taking time out to referee a 3 year old and 1 year old while cooking dinner). An indulgence, but not ridiculous given pasta is a relatively cheap foodstuff. Just buy it in bulk whenever it's on offer which is fairly often.
Heinz ketchup, baked beans and tomato soup. Will buy any other flavour soup based on what is on offer, but it has to be Heinz cream of tomato after experimentation with others!
Clipper tea - I'm very particular about tea and this is the least bitter tasting one.
Kelloggs cornflakes. Pretty much every other cereal has a good own brand equivalent which we get, but it has to be Kelloggs cornflakes to feel proper!
DH would add Branston Pickle to that list. I hate the stuff!
Free range chicken. I buy chicken thighs or whole chickens a lot and very rarely buy chicken breasts as that is a cheaper way of having free range meat. I have also started to buy free range turkey as it is a lot cheaper than chicken.
I buy a lot of supermarket and secondhand clothes for the DCs or use handmedowns, but I prefer to use a decent independent shoe shop while they are so little and their feet growing so quickly. It does mean DS only has one pair of shoes, one pair of wellies and some croc things at any one time though, rather than a different pair for each outfit!
I think pretty much everything else I will go with the deals or buy own brand. I buy own brand washing powder and cleaners as they do the job fine for us, and all those things like cling film, foil etc.
I'm also not fussed about my fruit and veg looking uniform so will buy the economy bags of onions that are different sizes etc. I also tend to bag up loose veg myself rather than buying prepacked as they are often quite a lot cheaper per kg.