I save the bits of vegetables not used in the Sunday roast, e.g. broccolli stalk, cabbage core, carrot peel and whizz them up in the food processor then freeze. I use this in my bolognese as a padding so I only use about 150g mince. It keeps the cost down and means the children are getting lots of vegetables without realising it. One of my friends' children will only eat my bolognese as he 'doesn't like' vegetables!