Make a list of everything you have in your freezer and cupboards and plan your meals around that before going and stocking up. Do this for evening meals and lunches
Another £2 coin saver here. If you can't trust yourself not to spend them, put them in one of those money tins that you need a tin opener to open
Topcashback and quidco
One that I've started doing is buying a 3 litre bottle of diet coke from Iceland for £2 and filling 6 x 500ml bottles with it. I get 6 bottles for the price of 2 (don't flame me for my diet coke habit lol).
Yellow label shopping and plenty of freezer space
Batch cooking look carefully in supermarkets at "offers". Quite often they'll have say a jar of mayo for £1.50 on offer but the next size up will be as cheap or a few pennies more expensive!
Make use of places like B&M and Home Bargains for everyday items - the teabags I buy are around £3-4 in most supermarkets but £1.99 in B&M!
Places like Lidl and Aldi sell multipacks of crisps very cheaply and are quite often nicer than the branded stuff (I prefer Lidl but that's down to personal choice)
As another poster said, if you're able to, grow your own veg and fruit. Saves a fortune in terms of strawberries, raspberries, cucumbers, tomatoes, potatoes, beetroot and anything else you eat a lot of! You will never get a better tasting piece of fruit/veg when you've just picked it
If you get through a lot of potatoes, consider buying them from a local farm - I get them at £5 for 25kg and kept in a cool dark place they'll last ages.
Don't be scared of "wonky" fruit and veg in the supermarkets. There's absolutely nothing wrong with them other than they don't conform to society ideal images
Always keep a bag each of self raising and plain flour in the cupboard. You never know when it will come in handy
Walk more. It's free and good for you and saves money on petrol / parking or bus fare
Half an hour a week is all it takes to get yourself into good habits 😀