Carry blank name tags in your wallet, coat, briefcase, and/or car. When an idea strikes, simply write it down on a blank name tag. When you get home, you can peel and stick the comment or note into your outline, journal, edits, notes, or sketchbook, without having to rewrite anything.
Bonus: They are small, lightweight, and not expensive. If one gets destroyed, toss it out without feeling bad.