Left over icing - if it's fondant icing (which I'm assuming it is) then you can roll it into little balls and make microwave meringues! Handy for crunching up over ice-cream or throwing together a pavlova if you make them big enough...
Just roll the icing into about the size of a golf ball (or smaller as that's actually quite big) put it on greaseproof paper and then whack it on the highest setting in your microwave for about 15 seconds.
You may have to adjust the above for your microwave, but you'll get light and airy meringues, not chewy ones, which are perfect for a quick pavlova (and you'll be able to eat the icing, then, as the eggs are cooked
)