Some of the best ideas I come up with occur at a restaurant with a friend, in the middle of the night, or gasp, while driving. Hence, the napkin, a journal and Siri.
The Napkin: Ok so it's not big, but it's effective. That's what she said. Wait, what?
Journals: No, they are not just for sweet sixteens and high school prom queens. There is a real advantage to having a notebook/journal where you can write down and keep track of all your ideas. I have one for WestSide Culture. There are many a nights where I'm tossing and turning in bed with an incredible idea. I've found the only way to eliminate that unwanted surge of energy is to write it down immediately. Come back to it the next morning at your local coffee shop and expand.
Siri: Siri has saved my ass many times in the last month. Grocery lists, errands, requests from the girlfriend that I agree to when not fully listening, they all add up. It's great to have a place to keep track of them and better yet someone (or something) to remember for you. I'll pepper her with business ideas and she'll remind me when I have a chance to explore it further.
Bottom line: (ugghh, yuck, corporate speak...sorry) You need to write down your ideas. You might think you'll remember them later. You won't. Do yourself a favor. Write it down in a centralized place you will be sure to look at frequently. Review it often to see how you are progressing.