Personal journals vary as much as people do, Thomas Mallon's collection of journals, A Book Of Ones Own divides them into 6 categories and is an excellent guide to how and why people keep journals. He keeps a journal himself. His father is a good example of an unwritten journal:
"My father never kept a diary, but he never threw away a canceled cheque either. When he died a few years ago I came across thousands of them in perfect order in a series of shoeboxes. Amidst stacks of others that took the family from the children's milk through his own bifocals, I found the one that paid the doctor who delivered me. My father knew they didn't audit you for 1951 in 1980: he kept those checks for another reason."
Page XV, introduction
A book of one's own, people and their diaries
This book came out in 1984 and without going though all my handwritten books I don't know when I read it. Now I use a differnt format for my journals, a computer program called The Journal http://www.davidrm.com/thejournal/ I highly recommend it. There is a one month trial, and then a 50.00 or so charge, buy a flash drive and install the program and your files on it, another level of security and you can carry it with you and use the calendar. I like the word processor better than Microsoft Word.