and a pen. Take notes.
Having worked for over a decade in management consulting, and now having been running this startup marathon for over three years, I always am bewildered by people that show up to meetings completely empty-handed. Bring a notebook. Always. Perhaps the training I received in consulting was just that good. Perhaps it's training that everyone should follow.
An "Employer" perspective: I once worked with this bright engineer who would nod vigorously in meetings, actively and delightfully participate in product meetings, and then a few hours after the meeting, have no recollection of what the meeting was about. We suggested she bring a notebook and take notes during the meeting to help - she never did. We soon parted ways.
Here's an "Employee" perspective: One of my first memories working at a "Big 4" management consulting firm was sitting in a very large intimidating conference room with the CFO and my firm's Partner level "big wigs". I was an Associate sitting in the back with the other Associates all furiously writing notes. At one point during the meeting, the client pointed to one of our Partners and then to one of the Associates that had stopped typing. A few moments later, he (that Associate) was escorted out of the room because he was not "adding any value" just sitting there. I learned at that moment, never let your guard down in meetings and always strive to add value.
Simply put: Bring a notebook, and take notes = you will auto-magically become WAY more effective.
Always take notes in these 3 situations:
If you're not used to carrying around a pen/paper always, other ways of accomplishing the same effect are: 1) add calendar items toward the end of the day and take notes in there, 2) send yourself emails with the notes, 3) voice record the meeting (not recommended for many reasons.) If I'm at a party for instance, and a situation comes up where I need a quick note, I will send myself emails when I'm not with my notebook.
My favorite method now is to carry a large black artist's sketchbook filled with large sheets of blank paper. I write notes, I draw arrows and connect meetings and thoughts. I emphasize some notes with extra underlines, circles and asterisks. Always bring a notebook.