Mostly in advance, more or less. I can only do one big shop a week so I tend to plan roughly as I am in the Supermarket and buy enough for meals for the week. I do have a basic cupboard ingredients so some things mnight vary. i.e. I buy mince but may not decide until the day whether we are having mince cobbler/mince in yorkshire puddings/mince with mash/spag bol/chili/meatballs with pasta/burgers etc. I'll buy chicken pieces but they might be a stir fry or curry or something - I try to have a rough idea in case I need fresh stuff e.g veg for stir fry etc.