I'll use a pocket-sized notebook from time to time. Usually, though, I don't have it with me so I'll use a text message on my phone and save it as a draft. Totally get what you mean about getting ideas when I'm not able to write -- that happens -all- the time.
^ I know, I know. My Dad tells me that every time I see him. Actually, I'll spend a night taking photos of each individual page *yawn*, because I'm too cheap to pay for paper and photocopying. It's just so many pages! And yes, Patrick94, I'm doing this draft by hand.