Dairy is thrown away earlier than almost any other food, usually on the strength of a printed date rather than a smell. Most of it has several days and several uses left, and some of it is actually better slightly sour than it was fresh.
Sour and spoiled are not the same thing
Milk that has turned slightly acidic but smells clean and tangy is soured, and soured milk is an ingredient: it makes pancakes, scones, soda bread and cakes rise better than fresh milk does, because the acid reacts with bicarbonate. Spoiled milk smells wrong rather than sharp, and separates into lumps and watery liquid. That goes. The distinction is made with your nose, not with the date on the carton.
Milk that needs using
Turn it into something that keeps longer: a white sauce for a bake, a custard, rice pudding, a batch of pancakes, or a soup base. Each of those buys another few days. Or freeze it. Milk freezes well in a container with room to expand, separates slightly on thawing, and comes back together with a shake. It is fine for cooking, tea and baking afterwards.
Yoghurt and cream near the end
Yoghurt going sharp is a marinade — the acid tenderises chicken and lamb overnight — and the liquid in flatbreads, cakes and scones. Stirred into a soup or curry off the heat, it thickens and enriches. Cream that is thickening is closer to crème fraîche than to a problem. Use it in a pasta sauce, a mash, a soup, or whip it while it still will. Cream also freezes, though only for cooking afterwards, not for whipping.
Cheese, which almost never needs throwing away
Hard cheese with a spot of mould can have the mould cut generously away, because the density stops it spreading. Soft cheese with mould goes entirely — in soft food, what you see is not all there is. Dried-out hard cheese grates, and grated cheese freezes loose in a bag. Rinds go in the stock or soup pot. Odd ends of several cheeses melted together are a sauce, a toastie or a filling.
Store it where the fridge is actually cold
The door is the warmest part of a fridge and swings through a temperature change every time it opens, which is exactly why milk kept there goes off first. Put dairy on a middle or lower shelf and it lasts noticeably longer. And close the lid properly. Dairy absorbs the smell of everything near it, and yoghurt that tastes of onion gets thrown away just as surely as yoghurt that has gone off.
Smell it rather than reading it, treat souring as a stage and not a failure, and freeze what you cannot reach in time. Very little dairy genuinely has to be poured away.