I do a monthly plan and a monthly shop for all staple items (fresh fruit, veg and milk get delivered every week.)Until recently, I planned everything for the month, even snacks and drinks. It works really well, as long as you stick to it and it definitely saves money because you can see exactly what you have and what you need. I have to be a bit more flexible, now, because I never know what is coming in my boxes, but even then I still plan a month at a time for staple meals and then fit my box in with what I have already. For example, I will plan to make a risotto one day and will use whatever suitable veg comes, same with soup, quiche, crumble (sweet or savoury) etc.
Your best bet is to plan multi purpose meals that you can spread out over the month. Some I make are:
chill, make a big batch and have it with rice or in chilli cheese subs one night, make a chilli dog bake and a tortilla pie for the freezer.
Chick peas, cook a big batch serve some with couscous cooked in OJ with onions, flaked almonds and dried berries. freeze some for spicy chick peas and chick pea burgers later in the month.
Pinto beans; serve some with rice, bread, sour cream and grated cheese, freeze some for refried beans to make quesadillas
Spicy split pea soup, freeze the rest to eat as curry later.
meat balls and hm pasta sauce, freeze seperately for all sorts of things during the month.
cooked chicken, freeze in meal sized portions and use during the month to make curry, pie, pasta bake etc.
If you work it like that, planning monthly is really easy and works well.
Hope this helps.