It is interesting the different ways people do this sort of thing.

Here is a bit more info about my method. It is pretty informal and I find it easy.

We have a whiteboard where we write down things as we run out. I usually shop on Mondays and before we go I check the whiteboard and look through the fridge, freezer and cupboard. I take note of things that need to be used soon. I think about the number of dinners we need that week and I write down the ingredients to be bought. This only takes a few minutes.

These are the things that make it easier and more flexible for me...

Breakfasts and lunches are usually the same so that is just milk, cereal, fruit, yogurt, bread, cheese, etc. Bacon and eggs on the weekend.

When I'm cooking things that keep or freeze well I don't just cook dinner for two. The other night I made apricot chicken and I made enough for 4 so we had it 2 nights in a row. Otherwise I might freeze half. Or a similar thing is that today I'm making bolognese, which I will turn into 2 lasagnes. One we will eat tonight, one will go in the freezer and there should still be enough bolognese left so I will freeze enough for 2 serves of pasta.

I'm not locked into meals in advance because I plan for some frozen and pantry meals. My bolognese in the freezer makes a quick and easy meal with a bag of dried pasta from my pantry. I also make risotto with frozen peas and bacon, all the ingredients are staple items from pantry and fridge.

I sometimes leave a dinner blank on my shopping list so I can be inspired by what I find at the shops, or I will modify my list if I see some good specials at the shop.

I also have tupperware fruit and veg storage containers, I think they are called fridge smart. They keep things fresh for longer, so if I decide to get take away rather than cutting up lots of veg for a stir fry the veg will still be fresh for another time.

That ended up being long, but I hope it helps. It is my informal method of having flexibility and good food without spending too much time at the shops and in the kitchen.