Got to stop guessing on quantities

I have never been an exact cook - a bit of this and a bit of that for about that long. However - I find that my approximate approach to recipes means that I often over buy by a couple of portions. I carefully store the leftovers intending to eat them the next day - when low and behold they get forgotten behind something in the fridge and have to be thrown away or at the dog - what a waste of money!! But things are going to change!!! I have just discovered this great tool devised by the Love food Hate Waste campaign http://england.lovefoodhatewaste.com/portions/everyday It works out how much of different ingredients you need to buy. Now, I have 3 boys who eat way more than I do so I put in 5 adults rather than 2 plus 3 children and this seems to work for us. Over the next 2 weeks I am going to use it to see if I can eliminate food waste all together. I would love to hear your top tips for avoiding food waste