We have menu planned for the last few weeks and bought only what we need, I did it online so I didn't buy random things like doughnuts or hot bread we don't need. I cook from scratch most days anyway except for the occasional curry. I have cut our shopping for a big shop of £80ish and a number of little £10-£30 shops a week to just the 1 online shop of £75 and then 1 loaf of bread extra from the farmshop.
We have halved out shopping bill and are not wasting as much food. DH and I sit down on a Saturday and make a menu then I sort out the ingredients for each, check what we have in then order at mysupermarket.co.uk and have it delivered from where ever is cheapest. I can often find free delivery code online too.
We don't plan meals but have a rough idea what we are going to eat for a couple of meals during the week. We used to shop at Morrisons or Asda and buy all our food from one shop. Now we shop in different stores. We got to Aldi, Lidl,Iceland, Asda and the local butchers. We buy certain things from different shops and we have halfed our shopping bill! I still buy some brand things like soap powder and shampoo but things like beans i buy aldi's at 34p 1/2 the price of heinz and they are nicer than the supermarket cheaper brands. By going to the different shops you also get to see what things are on offer. I buy milk and bread from Asda as they are not that cheap in the other shops.