How many times have you made a trip to the supermarket with a mind just to buy one item and come out with much more than that? More times than you think, supermarkets are designed for you to buy more than you need. How can you avoid being taken for a multi buy ride when you intention from the outset was for one item?
The firs thing to think about is do you really need to go to the supermarket fro one item in the first place. Think of the petrol you are wasting for a start, it is not just the cost of that one item it is time and money getting there and back. You may have a neighbour next door that can borrow you that item which will be replaced next time you bulk shop.
If you really have to go and buy that one item, don't take a shopping trolley, go empty handed into the supermarket and make a beeline for that particular item. Don't take the kids, they will be another distraction for buying extras not needed.
If you are not in a rush, take a walk or ride a bike to the store, this again will make you think about how much you have to carry, save on fuel and of course give you a little exercise - all positive steps.
Only take the amount of money you know that single item will cost and no credit cards, this again will literally force you just to buy that single item you had planned in the first place.
It is all about 'fighting' against supermarket tactics to make you spend more than you need to and if you take steps to counteract this you will have more money in your pocket more than you realise at the end of the month.