I have multiple planners and journals, and I usually have one planner and one journal in use. I say usually because now I am experimenting with a whole new thing (to me). I am keeping an Everything Journal.
In it, I have an art journal, poetry, a written journal, calendar, planner, scrapbook, smashbook, everything. I have started mine on Monday and I have to say, it is transforming my life, a little more every day.