So I have a notebook similar to this, where I create tabs at the top for "city/towns" - so for example if they're in "Port Nayr" - I will create a tab for the town. And inside of there, write down notable things and then highlight them with different highlighters (Orange = Taverns, Blue = People, etc). And this is also where I generally jot down notes and ideas (sometimes the players will say or do something that inspires a potential adventure, so I will quickly scribble it down and keep the game going, so I can look back at it after the game session and see if I want to do something with it).
But for NPCs, I typically do the name, race, hair & eye color (just for flavor) - general appearance (beard? Scruffy? Shapely woman? Thin woman? Motherly?), and anything notable ("married to the owner of the Lion's Pride Inn & Tavern, Marcus"), etc.
As for not being tied to a laptop - can I offer a counter to that? One of the best things I use/tools at my disposal (aside from my imagination) is TableTopAudio.com - I can't emphasize enough how much that can often help set a mood.