what do you do when inspiration strikes?

The thing about being a writer is that sometimes it's very inconvenient when inspiration strikes you. I know you can set aside a time to write everyday, but more often than not it seems that an idea finds you when you're not looking. So what do you do? I am fortunate enough that if I'm in bed and I think of something to add to a story, I can usually remember it come morning. But sometimes I lie awake thinking about it for a long time, so I might as well get up and write it down. But if it's a new idea, I find that I have to write it down almost immediately. I've bought tons and tons of notebooks, and I've tried to get into the habit of carrying them around with me. But the other day I had a line that was in perfect iambic pentameter, and nothing to write it on but a paper towel from the bathroom. I think the craziest thing is when I find myself writing a whole plot outline, character sketch, or anything else down while I'm DRIVING. Hey, stoplights afford you enough time to get a few sentences out before you become a danger to yourself or others...