Eggs I always buy free-range because yeah it makes a difference to taste (and is so much kinder to the chickens), but in the UK butter is butter. I know in the US you have butter that's practically white but here's it's all yellow and tasty. Flour every brand has plain, self raising and bread flour and those categories are pretty similar across brands.
Milk, the filtered stuff (Cravendale or similar) is nicer but not much nicer so it's not worth the upgrade IMO