i carry one everywhere i go, so if i have an idea, an observation, or just want to spontaneously journal out in the wildy, i write it down in the book! i enjoy writing with a nice pen vs typing on my phone and it's kind of therapeutic? it makes you feel more present with your thoughts since there are no notifications to distract you! also you get to practice your hand writing!
the pocket notebooks i use are field notes (grid) and moleskine (blank)
i also love writing with muji pens hehe