Drivers diary

Hey all, I have read somewhere on here that some drivers write a little diary for each day. I’m going for my class 1 training a the beginning of next month and I think I will try and keep a diary of my day as well as I also read that it can be used as back up for any problems that may occur. I can’t find the thread that I read about the diaries so was wondering what kind of things do people write in then. From memory all I can remember is time of starting, start mileage, end mileage, load but can’t remember what else. Any ideas would be great thanks