I often find myself carrying multiples of what is more or less the same notebook. Or at least using multiples of the same notebook.
I have both sizes of the travelers notebook. Plus that I often have three Rhodia A5 pads with perforated pages. Two ring bound, and one of the stable bound. Where one of each are dot grid and one lined.
And in the past I’ve carried multiple of the staple or ring bound models in different colors.
The reason I like them to be different is to make it as easy as possible to pick the right one. Lined versus dot grid is easy enough. And the reason that I sometimes use ring bound and sometimes top stabled is because they’re both good for different use cases.
The top stapled is great because of how easy it is to just tear off pages as I’m done with it. But it is terrible for any use where you don’t immediately tear out pages before starting on the next. So, when I don’t do that, I go for a ring bound.