What I write on/in depends where I am/ what there *is* to write on, usually. Which is why I tend to get to work with screeds of dialogue written all over my palm and (once at least) up my wrist. (It was for my verse retelling of Cyberwoman! It was important!) I do try and carry a pad, but I've also been known to write on tissues. And sheets of kitchen towel. And loo roll, and old receipts. Those are better, although it gets a bit fiddly around the VAT number and printing. I don't forget and lean my cheek on those, and then have backwards writing on my face...