Journals are items found in desks and bookcakes of many houses, but can also be found in crates and in kitchen containers. You can use a Pen or a Pencil to write text on it. This is useful to write down important things to remember, like where to find loot you dropped. Journals are similar to notebooks, however a journal contains 20 pages to write on, compared to a notebook which has 10. Doesn't reduce stress, boredom, or unhappiness.
It can be renamed and used to leave messages in Multiplayer servers.