I love this thread!
One of the best money saving tips I have ever received was via Mumsnet - when making a chilli or bolognese etc, half the mince you'd use and top up with lentils instead. I use 250g with 100g dried red lentils in a dish where I'd usually use 500g mince and it makes 4 generous portions. Freeze the remaining 250g mince for another 4 person meal! Good compromise if you have fussy eaters who miss the meat in fully veggie meals.
I think my best tip is learn to cook and the frugal stuff comes easily. You can go far with Basics/Value chopped tomatoes, kidney beans, baked beans rinsed to use in the place of expensive haricot/cannelini beans etc. You just can't justify buying branded cupboard essentials like this when on a budget because when it's all boiled up it tastes the same. Especially if you learn how to season well. Look at recipes and see what can be substituted for Basics ingredients or left out altogether. It's not worth adding that one single strand of saffron at £2 if it's going to triple the cost of the meal. My SIL is a bit of a Waitrose snob and absolutely loves my cooking, completely unaware it's Basics/Lidl products!
Freeze anything that's going off for another day. I always cook double for us 2 and then have two portions for packed lunch the next day. I have a scrapings pot in the freezer for any decent plate leftovers which will be added when I make a veggie chilli as it all boils down together. DP always goes mad for it when I make it and she can be snobby about no meat or leftovers.
Build up a spice store cupboard and buy your dried herbs and spices from the Asian aisle too - you'll get a 100g bag of spice for around 80p when the 30g glass pots you'll get from the supermarket brand are about £1.
I'll second the Sainsbury's Basics range - especially the tea bags. I think they're 30p now. A well off friend came to visit, tried them and loved them so much she made us take us to Sainsbury's to pick some up for home! My weekly shop always contains their Basics bubble bath, flour, chocolate for baking, Greek salad cheese (better than feta), chopped tomatoes, kidney beans, bin bags, peppers and we eat well with lots of veggies and scratch cooked food. Buying a delivery pass and getting shopping delivered has saved a lot of waste, unnecessary purchases and hassle.
Frozen veggies are great. My fave is frozen spinach. You can whack a couple of cubes into just about every one pot meal and it gives a good vitamin boost.
Love her or hate her, Jack Monroe's blog has some great bargain recipes that are all easily tweaked to add or take away ingredients you have leftover/don't have. Some are a bit crap and it's a bit trial and error, but her mushroom stroganoff, vegetarian chilli, veggie bean burgers, tarka daal and sag aloo are huge favourites here. Just remember to season much more than she suggests.
People that haven't tried baking bread before - Delia's basic white and brown loaves are dead easy and involve minimal faffing. Always come out well even using Basics flour and Lidl yeast too.
I love my slow cooker. The main thing I use it for these days is bubbling away for a few hours on high cooking something I'd otherwise be watching constantly on the hob. I also got a cheap timer plug from Argos if I don't want it to overcook. Mine has a lightweight metal insert so you can start off the dish by frying and then transfer the whole thing to the heating element. It's so much less clunky and cleans like a dream and the non stick is still going strong after nearly two years. Think I paid about £20 for it on Amazon.
Try out non-branded products to see what you like. I can use most supermarket own brands on toiletries etc, but still use Simple moisturiser. But I only buy it when it's on offer - it's usually £2 somewhere and lasts ages. I remember the glory days when it was buy 1, get 2 free at Tesco! Same for Heinz ketchup. The Aldi fake Touché Eclait concealer is as good as the real thing. Boots own brand 75p shampoo and conditioner and curl cream is great. A friend who has the nicest hair I've ever seen once admitted she uses Tesco's cheap brand at 50p a large bottle so it just goes to show!
Proper coffee lovers - I buy the bags of Lidl ground French or Italian coffee. Put it in a 2 litre jug and fill with water to the top. Leave out overnight on the countertop. Strain it in a strainer with a bit of kitchen roll in into a pouring container that will fit in the fridge (always available in Poundland). You then have for £1.75 about 20 servings of cold brew coffee concentrate - what they charge £3.75 PER SERVING for in Starbucks. It's much less bitter too! Keep it in the fridge. When you want a hot coffee, pour about an inch into a mug and top off with boiled water. Instant Americano! For an iced coffee, I put an inch in a glass and top up glass with ice and add milk to the top. It's honestly so good, portable to work in a plastic coffee cup and will save you pounds and pounds. It lasts me a week to two in the fridge and I drink one to two a day.
I'm terrible for buying stuff I don't need by mindlessly using my contactless card. If I take out cash of a limited amount for the month and budget for cheaper weeks and more expensive weeks, I spend much less and actually enjoy saving a little.
Lastly, ease yourself into it. There's no point buying dirt cheap stuff that you'll end up throwing away and getting a takeaway. Beware of false economies. I have countless friends who've decided they can't afford the £8 a day Pret lunches any more and instead spend £2 on ingredients to make a bland soup that's supposed to last them a whole week. They usually last 2 days before it ends up in the bin and they're buying expensive food again. Try things and don't buy again the stuff you didn't like. You can do it and it'll become second nature. And this is coming from a previously wasteful crazy spender so anything is possible.