Material Ideas
Henri Matisse Cut Outs
How to use Instagram to create a colour palette
The images below show one way to make a colour palette, just by using your phone. You can use other apps, design software, MS Paint, or actual paint, pens, or pencils. Whatever works for you and communicates your colours, so I can use them in the collages.
Artist Andy Goldsworthy
Goldsworthy creates artworks in the natural environment from things he finds. This article has tons of pictures of his work, which may inspire you to create something similar.