Maybe it could be a place where you put your food and exercise in. Like:

1 apple = so many calories
1 sandwich = so many calories
so on
so on

Total = so many calories

Ran 1 mile

I could also use this diary to talk about my Wild Cats and how they drive me crazy!
"Dear Diary, today one Wild Cat said I was an old woman. One said I was crazy. Thanks for listening dear Diary."