Liz Gilbert (Eat, Pray Love) does the same, but with a jar. A great big glass “happiness jar”. Every day she writes the best thing that happened on a scrap of paper and throws it in the jar. (google it, you’ll find pics) — then when she’s down, she can start pulling out scraps of paper and reading them. Either way, I think it’s a really great project to try at least once. I use a plain notebook.