Pictured above are my current absolute essentials in my day to day life as a writer.
I say current, because the container may vary, but I always have a pencil case, a planner and a notebook. That doesn't change, or if it does, it doesn't change for long.
The pencil case has scissors, a ruler, refills, glue and such. I use all of those on a daily basis.
The planner (a Filofax Pocket Malden in purple, for my fellow planner nerds) has my to do list, planning, daily pages, a writing journal and brainstorm section and such and lists.
And the notebook (always decorated) is for everything else: journaling, poetry, glueing in everything to do with my day etc.
I carry all of these no matter where, but if I want to travel light, I usually bring my journal and a roll of tape to stick in interesting bits I find along the way. Sometimes, I even write scenes for my stories in my journal. If I have something for my planner, I write it in the back, and add it when home.
For me as a writer, both are essential tools.
I use my planner to plan my day, to keep my mind calm. I take notes in it during writing, and at the end of the day I write a progress log (something I learned from Writing on Both Sides of the Brain by Henriette Klauser).
And my journal is for every day life. If I have thoughts meandering through my head I usually journal for a bit to process everything, or if something funny happens and I have to jot it down immediately.
My journals are my happy place. I don't usually write negative stuff in there, I have separate pieces of paper for that so I can shred them afterward. This ensures that each journal is a joy to flip through again.
All this ensures that my journal also works to bring me to a calm mental state, which is a pretty good point to start my daily writing sessions from.
I've also noticed that if I don't plan or journal daily, my writing inevitably slacks. This is why, no matter how much I don't wanna, every day, there is something in both, even if it's just a post-it with some notes.
Perfect, for me.