One thing I like about the GTD system in a planner is that I can follow the guidelines but still use my own personal taste as far as insert design goes. Brandy Michelle Plans on YouTube uses the GTD system and vlogs extensively about it. I recommend checking out her channel. Here style has changed over the years as far as her daily pages go, but as far as I can tell she is using 2 days on 1 page and while I am getting used to a new system, I'm trying to do things the way she does. I made the inserts below, she has similar inserts available in her etsy shop.
My usual daily pages (in my half size planner) usually has a lot going on - tracking water, meals, appointments, to do's - and it's all over the place. I do like that, but for now, I like doing my pages bullet style and I still track all those things - just differently. The circles down the side of Monday is how I tracked water, and the heart was to check off when I exercised. I might write dinner down on one line or just refer to my inbox where I wrote the menu when I as planning my grocery list.
I made the today marker from some letter size dividers I bought at Target ($2.99 with plenty left over for more page markers, dividers, and even dashboards. The brand is Yoobi.