A Rocket needs to get off the ground in order for it to be called a Rocket and not just a heap of cardboard and plastic. When researching I found there was one suitably powerful yet safe chemical combination. KNO3 and Sugar, combined together and ignited at 300+ degrees provide enough thrust to lift off the ground.
There are numerous ways to prepare a batch of Rocket Motors. Different combinations provide different results, which means you can choose to prepare specifically different motors when building your rocket.