The pen used is a Kuretake Cocoiro brush tip in black.
Each day, I would write down the things I saw in bullet points. I even noted down how many steps I did and the distance walked (according to my iPhone's health app). If something funny happened, I would also note that down briefly.
I kept all receipts so that I could document how much I spent in Stockholm. This is important me on two levels - it helped me stay within budget and also check my credit card when I came home, just to make sure nothing unexpected appeared on my monthly statement.
This'll all come in handy when I finally make my travel journal from Stockholm. I got some photos printed and all I need to do now is to stick them in and write a blurb about each of them. That'll be a job during the Christmas holidays I'm sure, depending on how much free time I have! A post on that to follow at some point in the near future :)