When I visited my parents in the Czech republic, I restocked my supply of sketchbooks. I use these colourful no name sketchbooks (I would have bought pitch black but they are always the first one to be sold out). It would have been nice to have some fancy sketchbooks like Leuchtturm 1917 or Moleskine. However, that would probably lead to fear of writing or sketching in such a nice sketchbooks. And that is the exact opposite of what I want to. Sketchbooks are born to be filled with messy notes and quick drawings, half-baked ideas and random thoughts.
And these ideas may later be revisited again, remembered upon and refined when their time comes.
People from all areas of knowledge have many great ideas. They come in various times, during various activities. One may come up with an interesting idea during commute by train, someone else has great ideas during morning run and someone has the best ideas late at night. We do not know when the idea strikes. Our mind is working nonstop even when we are not aware of it. And is filled with all the things that bother us. It is not unusual to spend whole evening trying to figure out some answer to a problem only to wake up in the morning with the answer appearing as the first spark of the woken up brain.
Some ideas are practical, some idealistic and sketchbooks are there to capture them all. So it does not matter what you do, I encourage you to carry a sketchbook with you all the time, you never know when the idea sparks.
And for that you need your sketchbook. It can be simple school notebook, fancy Moleskine, or when nothing else is to your disposal sketch on a napkin, just catch your idea until it dissapears.