99% of my 'emergency writing' I do with a ballpoint pen on a steno sized notebook, usually at the scene of a fire or flood. Notes are important to make sure you don't miss anyone, and good for writing reports too. When I fill up a notebook, it goes in my file drawer. I have to pull them out from time to time to address info requests. Just about any pen will do, I keep several in my Red Cross vest and an inordinate number in my carry bags.

1% of my emergency writing comes with a sharpie marker on athletic tape affixed to my thigh - during CERT searches and triaging first aid you're taught to account for who and what you find, and that can be as simple as logging wounded and KIAs, or more complex it could be noting the room number and number of victims, or the vitals of a patient. I've trained at this and it works, and keeps your hands more available for work than a steno book or piece of paper. But its all been training so far, although I still keep a roll of tape and sharpie in my RC turn out bag, and steno pad and pen in my CERT gear.

Buy the little stubby sharpie permanent markers, they're compact and portable and fit in First Aid Kits, and write on anything including athletic tape and paper.