A Field Notes notebook. Alternately, a Muji notebook of similar size. I use roughly a page per day (sometimes just half a page), laying out appointments/meetings as well as things I have to do. When I don't have that on me, Google Keep.
I've got this old Decomposition Book which has become a log for drawings, lyrics, and my stupid teenage adventures. It's such a valuable thing to have and I keep it in my backpack always. Field notes looks awesome, I just might try it out! Would be cool if they had the different kinds of paper all in sections of one book, though that might just end up being super inconvenient.
Yeah, they're rad. I totally recommend them. The paper is nice, the covers are pretty durable and you don't look half bad pulling one out of your pocket. They're also expensive. You're in NYC, yes? The Muji notebooks of same size don't have cool colors but they're half as much.