So my basic palette is:
Ultramarine Blue, Pthalo Blue , Raw Sienna, Cadmium Yellow, Cadmium Red, Alizarin Crimson and Burnt Sienna. Over the years I've also added Raw Umber, a lovely colour for NZ bush. And Australian Red Gold, a beautiful transparent orange. Most of those other colours that you can see in my palette have been sitting there in their dried state since I first tried them!
If you're reading this as a painter, I'd encourage you to simplify your palette and learn to mix what you need from that. A limited palette means a more harmonious painting in the end.
I'd be interested in your feedback on how you approach colour mixing....