I decided to try using the bullet journal system this year. (You can read about bullet journals here.)
Since I would be needing to write down stuff pretty quickly, I figured that it would be best to have a pen always handy. Unfortunately, the notebook that I decided to use does not come with a built-in pen holder. After a cursory saunter down Google lane, I failed to find a solution that I could do without first having to go out and buy stuff. (NOTE: There were interesting solutions, that required using gorilla/duct tape -- for instance here and here -- but I did not have any gorilla/duct tape on hand.)
The fix I ended up employing takes only a couple of minutes to do. All you need are a pair of scissors (or anything you can use to cut materials with) and a short length of whatever material you want to use for your holder. (NOTE: this solution is meant for notebooks with vertical elastic straps.)
Step 1: Cut a Length of Pen Holder Material
Find a length of material which you can use for your pen holder. In my case, I used a length of black material which I had cut from the handle of a recyclable shopping bag that was laying around the house. The length should be such as to allow the material to wrap around the pen that you want to use and also to extend a bit beyond the pen on both of the ends of the material. (NOTE: you may want to measure the dimensions of the pen.)
Step 2: Secure the Pen Holder to the Journal
Using tape, or any other adhesive, stick the pen holder onto either the back or the front cover of the notebook.
Step 3: Use the Pen Holder
To secure the pen onto the pen holder, just slide the pen under the elastic strap -- making sure to clip onto the same elastic strap -- and putting the pen through the pen holder..