I have been meal planning for a few months now - because I was shocked at how expensive my weekly bill was.
When it started nearing £180 regularly that was when I decided to have a long, hard look at things. There are 4 of us (dss are teenagers so eat adult portions) and 2 cats. And I buy a lot of wine each week
Now it's usually £40 sometimes even £50 less than that.
I meal plan, and usually include at least one vegetarian meal per week, to keep the cost down.
I've started buying cheaper cuts of meat, e.g. roasting a whole piece of belly pork rather than buying two pork fillets and where it makes sense (i.e. the product quality is just as good) I buy Sainsbury basics. Products such as their tinned tomatoes for example, or a string bag of courgettes. I can't see the difference between basics courgettes and their normal ones that are either loose or wrapped in plastic!
I buy more Sainsbury's own stuff - cat food pouches for instance are £1 per box cheaper. As I buy 2 or 3 boxes a week this has helped.
And on the wine front, I am buying cheaper wine. There was an offer this week for Spanish Gran Temperanillo (sp?) at only £2.99. They have also brought out a lower alcohol, with the brand name 10%, which (because it is lower alcohol) is slightly cheaper at £4.99 a bottle. And it's a bit better for me - or less bad!
But meal planning has definitely been the best thing - I only, only, only buy what I need for the week. It has also cut down hugely on the amount of stuff I was throwing away each week.