Over the years I've come to the conclusion that one of the most useful things that you can have with you is a small notepad where you allow yourself to write whatever needs to be written with no organization or structure at all. For the past couple months I've had a small Rite in the Rain notebook in my back pocket along with one of their pens and a notepad in my shirt pocket at work. I use these things almost every day and I can't imagine life without them.
I first began to realize the utility of small notepads like this during my time as a computer science student. Instructions and requirements for assignments would always be on webpages and I got tired of disrupting my workflow by constantly having to switch between my text editor and browser to make sure I was doing everything right. So one day I walked over to the store on campus and spent sixty cents on a little notepad and from then on whenever I'd get a new assignment the first thing I'd do would be to transfer the requirements from the assignment's webpage into a simple list in my notepad and any classes and data structures that were necessary for that assignment could also be easily worked out on that notepad. Then since I physically wrote out the requirements I could remember them much better and reference them much easier because they were in a format that worked for me. Then because it was on paper in front of me, rather than on a webpage I couldn't edit, I could also use that notepad as a checklist so I knew I wasn't forgetting anything before submitting that assignment.
The notepad was also great for drawing things out. When engineering software it is often helpful to draw out how things interact with each other to either explain it to someone or to make sure the idea that is in your head is actually feasible. Of course software exists that does this exact thing but paper and pen will always be more accessible for drawing than software ever will be since you don't have to spend time figuring out how it works, most of us have been using a pen and paper longer than we can remember as they are among the first non-toys that parents let children play with.
When I left the world of software development I also left behind my trusty notepad for a season because I never used it in the real world. But in the last few years I've gained the habit of always having a variety of useful things in my pockets and through researching preparedness and survival I decided that I should bring notepads back into my life. My work notepad is of course used for jotting down data I use for work but the one in my back pocket has filled many roles. I use it to write down addresses of places I need to go and directions to them, I've written down bolt sizes for car parts in it before I go to a junkyard to pull those parts so I don't have to lug around more tools than I need to, it fills in for my work notepad when the wind makes using something spiral bound too difficult to use, I've written down names of talks or verses of scripture that come up in church that I've wanted to look into at home, you can tear out a page to leave someone a note or mark a path. The utility of always having a small notebook with you (much like a dedicated flashlight) is something that you will never fully realize until you've come to rely on it.
Now can your phone do most of these things? Yes. But can it do these things as well? Not really. I'm sure there is at least one of you out there reading this who has a good note taking system on their phone that works for them but for most of us the process of taking out your phone, unlocking it, opening the notes app, starting a new note, and finally typing something in it is something that we rarely do and almost never actually refer to. Try replacing that function of your smartphone with a pocket notebook. You don't have to get fancy Rite in the Rain stuff like I did, you will be more effective at many things if you take the time to put the things you need on paper and you can't do that if you don't have a quality pen and paper with you.