I've only read the first 2 pages of this thread so far but I've thought of a couple of things I do that some may find helpful and I apologise immediately in case anyone has already mentioned them on pages 3-21.
Someone mentioned using the 'To good to go app. There's also Olio where people collect very short date food from stores and advertise it for free on the app. You can also get food that individual people have and don't want or even household items. I have away some breakfast Cereals if had a few or of and didn't like, dog food my dog didn't like, a fish tank, among plenty of other things and I've had a few bits from other people too.
I don't have a kettle, I have a machine that looks like a coffee machine but is only for water. It holds 4litres (almost 3 kettles worth) but only heats water as it dispenses it, so no boiling too much.
I never use a normal mug, I always use travel mugs, even at home. I'm disabled and prone to dropping things and I've been scalded by hot drinks far too many times, plus I was getting sick of having to clear up the coffee and the broken mugs. The travel mugs work great though because I'm also notorious for forgetting about a drink, then remembering it once it's cold, but now my coffee stays hot for several hours and is still warm (at a push) after 6hrs.
My son bought me a weighted blanket last crimbo and I find that's just as good as having an electric blanket, without the electricity cost.
In the summer I bought a couple of 50p packs of carrot seeds (from Wilko) which are now probably going to see me through most of the winter. I also threw some green looking potatoes into my compost bin and I've now got a lovely crop of potatoes too.
I buy a £3.70 bag of frozen stew beef in Asda, throw it with some veggies, a tin of baked beans (own brand, you don't need Heinz in a stew), oxos, etc into my electric pressure cooker and in less than 45mins I can get 4 or 5 decent servings out of it, I'll usually eat for 2 days and freeze the rest, but it should be enough for a family of 4.
I only cook with my electric pressure cooker, air fryer oven and microwave. This way everything cooks so much faster and more cheaply. I've not used my main oven or stove top in almost 3 years now.
All the lights in my house are 'smart' bulbs and I control them with my Alexa, so if I'm moving from room to room, i tell her to switch them on and off as i move around the house.
My heating thermostat is also WiFi controlled, so I can tell Alexa via my phone when I'm out to put the heating on when I'm on my way home, so it doesn't have to be on from a set time, especially if I'm out longer than planned, nor do i need to come into s cold house because I've decided not to put the heating on before i went out.
I'm planning to moving house next year and I'm currently looking at ceramic radiators rather than the ones connected to the boiler. These are electric, they heat up in a matter of minutes, you turn them off and they retain their heat for well over an hour. If I put smart plugs on them, I'll be able to control them by WiFi too.
I'm sure I can think of plenty of other money saving things but I think these will do for now.