I have never made ganache. Is it always equal amounts chopped chocolate and heavy cream? The recipes I have found make too much for my needs.
That's pretty much the formula I follow but you can customize to your needs. Some recipes call for a little butter or corn syrup.
You could freeze your leftovers or repurpose them. I think that ganache can be frozen and defrosted in the fridge. I'm sure that I've done that before.
You could freeze cubes to enhance your morning coffee - chocolate and cream + coffee = mocha :). Leftover ganache is fantastic on french toast. It would probably be really delicious as the surprise filling in banana bread muffins.