Sections for top defenses in D&D (1st and 10, 2nd/3rd and long, 3rd and short, 3rd and medium), top situational defenses (end of half/quarter, pressure package, red zone, goal line), and maybe by coverage.
I have a buddy who has coached college for a number of years and he talked about how defensively they had certain calls to "highlight" specific stud players as well. Mainly stunts to get them in a good position for a sack or calls that leave them free to roam or something I think.
"Knowing you have a good backup long snapper allows you to sleep good at night." - Bill Belichick
I create a call sheet. One side has their tendencies on each down and distance situation. The other side has my top 3 calls in each of those situations. But in all honesty I hardly use it. I already know the gameplan and know what I wanna call. And as the game goes on it becomes as much about feel as it does anything else.
For example, Friday we played an opponent who had should 13 snaps in 10 personnel in 3 films. But in the second half and we got up some they were in it a significant amount more. So we began to play a lot of man free and rush 5. This was not part of our original plan. But the game dictated it.
I just enlarge the font of our card that goes in the kids wrist bands. Then I write with sharpie on it for situational stuff. I have had call sheets in the past where we broke down all kinds of stuff but we never really used most of it. I like it better now that I am looking at what the kids are looking at. Beyond the calls we put special personnel groupings and personnel for special teams that we are in charge of on defense. And in the margin we also put the gameday schedule so we don't have to carry around another sheet of paper.