I have planned my weekly menus, since I first started work and was living away from home. Supermarkets closed at 5pm so I could only do a food shop on Saturday. I also used to go down to the local Saturday market and stock up with fruit and veg and there was a marvellous butcher and cheese store there. The main thing is to build in some elasticity into your plan so if something happens you can do a quick replan.
I always start my weekly plan by surveying the fridge to see what needs to be used up, before writing out a plan, check the recipe for any meals that require one for that odd ingredient you always forget and do not forget to check your stock of any herb/spice you need. I have been caught out that way.
I also bulk cook. I will cook a casserole using a lb of meat and then put a portion on each plate and portion the rest into containers in the freezer. That way I currently have a stock of about 20 home made ready meals in the freezer, for days when I cannot be bothered or do not have time to cook.