Depends on the situation
If I have something to add to a meeting, then I'll have an @agenda-xxx list open so I don't forget to bring something up. If not, then i'll usually just have my capture tool (index cards or notepad) ready so I can capture important information that I need to remember or act on. Once the meeting is over, I'll add this information to my @action lists or reference, as needed.
The @action list is not dependent on whether or not you're by yourself. It's for whenever you need to reference the lists. I've brought it out when talking to someone (RTM app on my iPhone) and made a next action item right there on the spot. If anyone asks, I just say "I'm writing it down so I don't forget." Not only is it accepted, but sometimes people are appreciative that I felt it important enough to write it down.