Choose the meals you will actually cook this week, check what is already in the kitchen, and write the missing items. Buy those. The savings are usually in what you do not put in the basket: the extra sauce, the snack you were not hungry for, the ingredient that will spoil.
As an illustration, if unplanned extras run about 15 each shop and you shop weekly, that is roughly 60 a month. Your number will differ. Measure one shop with a list and one without if you want your own figure.
Start this week
Write four dinners on a card before the next shop, and do not add a fifth item that is not on the card.