One thing I always have with me is a black notebook. I take meetings notes in it, I do math in it, and when I need to organize my thoughts I write in it. I usually can’t even read what I wrote, but writing ideas down helps me think. I usually use a moleskine notebook, but my current notebook is an ecosystem notebook. It looks exactly like a moleskine notebook BUT made with 100% post-consumer recycled paper and uses soy-based inks.
One of the coolest features of this brand is that each notebook has a code, which you can use to find out the materials you notebook is made out of and where it was made. Here are these details for my notebook: 
The video they have on their website is pretty embarrassing. You won’t find my notebook around the city peeping out of my bags, resting on a friend’s shoulder or being played with by a baby. The most exciting place you’ll find me is scribbling away in a pleasantly, noisy coffee shop.