I started with a journal/notebook type of thing for my first two parents. That lasted a whole month maybe and I decided it was a waste of time. Anything that I put in there was normally discussed at the door anyways and when I asked questions, the parents didn't write back but instead just told me the next day at drop off or pick up. It seemed like extra work that I didn't need.
I've put a white board up at my front door and I will write what we eat on a daily basis there. I will also write if I need supplies from anybody and also days off. If there is anything else the parents want to know that day, they ask and if there is anything further for me to tell the parents, I tell them by mouth.