I don't really plan meals, just make sure I have lots of different ingredients in. We get the mahoosive sacks of spuds which usually lasts us a month. I get most of my fruit and veg weekly from the local market because it's much cheaper than the supermarket (e.g morrisons had a special offer on half a melon for £1 - the market stall sells a whole one for 80p!).
I love b&m for buying jars of sauces too - about 69-99p per jar and so much variety, we stock up on loads of those too. I go to the gym so use them as quick meals when I get home.
But things that last like tins, crisps, biscuits etc we go with whatever is on offer and stock up enough for the month then buy fresh/perishable stuff as and when needed.
For the 3 of us we spend about £130 a month on our big shop then odd bits here and there as needed for the rest of the month. I hate food shopping so much prefer to do it this way, I don't mind popping in for a couple of bits in the week if needed.