I write everything down in a notebook that I then take to the shops. We also have a blackboard in the kitchen that I write the menu on for the week. On the left-hand side of the page I list the days and what meal we'll have, on the right-hand side is the shopping list taking into account what we'll need for all the different meals and general grocery items. I also have an 'extras' section for all the baking, and extra things that need to be done, ice cream, stock, any cheese or yoghurt etc. Below the general grocery list I have two other sections, one for what we'll get from the dairy and one for the butcher. I normally get enough fruit and veg to tide us over until we go to the town markets on Thursday morning.
I absolutely feel lost without my menu plan, I get to 4 o'clock and freak out cause there is nothing out for dinner. I also wander aimlessly around the grocery and get a thousand things we don't need and forget the important things like cheese and chocolate!