Reddit reviews Moleskine Volant Notebook (Set of 2), Extra Small, Ruled, Antwerp Blue, Prussian Blue, Soft Cover (2.5 x 4)

Looks like your "log" was in the style of a Moleskine Volant (small field notes style notepad).

Lots of technical folks love them - I'm a web developer myself and keep them handy. They are usually that small and about 56 pages. All of that said, they are like two or three for $5. Not exactly a huge bonus, but at least a hint of geekiness.

I like to write the lessons that I've learned from such a situation( I use a Volant ).

I use allpro. Before i started, I worte down everything I needed in a tiny moleskin. cheap too. here you go

If you're wearing a blazer/jacket, you can always put it into the side pocket pretty discretely. With normal shirts, as long as the notebook isn't too large, it won't be much of an issue. Honestly, nobody will really look down on an otherwise great outfit because you have a small notebook in your front pocket.

Not sure if this is what you already have in the photo, but I've found these notebooks to be very small and discrete.