On a whim I created this palette – a sliver of an egg carton – so I could easily roam around the yard. I was inspired to play around with the different shades of green and different textures growing in the yard. I’m happy to be back at it after being away!
Have you read:
mycreativeresolution.com 
I usually use small watercolor set with palette on the lid. It’s because I also need a lot of water. It makes sense to adjust supplies to your personal needs. I also love having a good sketch. In order to get it done, I find pen very helpful.
Your portable palette is very interesting.
Thank you Inese. Glad to hear what works for you. I love using a pen too. I just use a sigma Uniball gel pen.