Yes I agree a freezer would be seen as a basic for many people. It does save us money. Once we open a jar of tomato paste, any excess is immediately put in ice cube trays and frozen. If I need a few tablespoons for cooking I just nudge out a couple of tomato paste ice cubes. I also keep all chicken trimmings in a bag in the freezer till I have enough to make chicken stock with a bit of carrot, onion and parsley which I freeze. (The fat rises to the top and solidifies so you can lift it off so don't worry about fat going into the scrap bag because it won't end up in the finished product.)
We do freeze milk as well. More convenient to do so in smaller bottles rather than trying to defrost 3 litres in an even way.
We freeze casseroles as I tend to cook double batches and freeze the extra. We don't have takeaways very often - fish and chips versus coq au vin in the freezer?
I have found that washing celery, drying it with a tea towel and wrapping it in foil in the refrigerator gives it near immortality. It stays crisp and green for a couple of weeks rather than becoming khaki and floppy within the week. Apparently, the same applies to broccoli but I haven't yet tried that personally.
If you forgot to get the celery prepared and stored and are confronted with the wilting remains, do not despair. Cut the stalks to usable size and soak in cold water for an hour or so and the celery will crisp up.
If you are suspicious that the that fish is not super fresh, soak it in some milk with a load of thyme in it, trim the ends of fillets (this bit is important) and it should taste delightfully fresh when you flour it and pan fry it. (I'm not talking about fish that is off here obviously - just the sort than can taste a little fishy.)
Parsley grows like a weed in our garden so I like to use a bit of that in most dishes as it gives it an extra green boost. Thankfully, we have the flat European version rather than the unpleasantly curly stuff. I am not sure about growing a lemon tree in the UK but they are a useful plant.
Anything that looks like it might go off before we get to eat it gets put in the freezer before it has a chance to go bad.
I have to confess though that my freezer is taller than me and I'm not short! Modern freezers simply don't have as much internal storage as in the past. When we redid our kitchen - it dated from the 1980s with red Formica and made builders chuckle - we found modern appliances were tiny inside.