Detail-Oriented
Antoine basically lets us know what kind of writing style we're in for when he begins his diary by saying he'll:
Keep a diary to see clearly—let none of the nuances or small happenings escape even though they might seem to mean nothing. (1.4)
In other words, be prepared to read a bunch of long descriptions of places, people, and events that may or may not have any significance to the overall plot of this book.
And before you get all angry about what Antoine is doing, just remember that no matter how bored you might get by all the details he lists, Antoine is ten times more bored. He admits this to us openly when he says:
From time to time I yawn so widely that tears roll down my cheek. It is a profound boredom, profound, the profound heart of existence, the very matter I am made of. I do not neglect myself, quite the contrary: this morning I took a bath and shaved. (31.5)
To put it simply, writing an exciting and interesting story is not Antoine's number one priority. His main interest lies in figuring out the nature of all existence, and you can't do that without paying really close attention to everything you experience.