I grew up in quite a large family and was used to seeing my parents buy in bulk. As this is generally the most economical way to shop I never really considered doing anything else when I left home and was responsible for my own groceries.
However, when there's just two of you, bulk buying just tends to end up with a lot of waste as bag after bag of 'buy one get one free' salad goes in the bin followed by half a block of mouldy cheddar and a punnet of mushy strawberries.
Throwing out food is not only expensive, I also feel that it is immoral. Who's mum hasn't said to them "Finish your food - there are children starving in Africa"? whilst whether you finish your lasagne or not will make absolutely no difference to whether people go hungry on the other side of the world, we need to remember just how lucky we are in the affluent West and endeavour to waste as little food as possible.