The best waste is of course no waste, but as long as that is a utopia, there is nothing better than coming up with creative ideas with waste materials.
One of the most beautiful sayings I ever saw was: Waste is only waste if you waste it.
And once you get used to thinking in terms of reusing and not wasting stuff, a huge flow of ideas will start, I can assure you.
In this article, I list a number of ideas for inspiration or imitation.