That awesome idea you just had? You aren't going to remember it in 10 minutes. I promise you. Get it out of your head and onto something a little more stable than the jelly-like organ that's working hard to keep you alive and not just remember your seemingly incredible ideas.

Your smartphone has a reminders or notes function. Use it. Bonus points for learning how to voice activate it. I can say "Remind me to do X," to my phone and it will automatically add it to my Things inbox.
Small notebook, back pocket. Small pen, front left pocket. This may only work for the fellas but it's relatively easy to carry a small notebook (Field Notes or Moleskine are good) in your back pocket and a small pen (like a Space pen) clipped to the inside of a front pocket.
Use some kind of software on your computer that makes it easy to quickly record an idea. I use Things which allows me to hit CTRL + OPT + SPACEBAR to bring up a quick entry box that will immediately put whatever I type into it in my Things inbox. This plus muscle memory will allow you to record every good idea without overly distracting you from the task at hand.