I already wrote my September 11th experience here. Rather than rehash everything, the link is here if you feel like reading about it.
That post is from five years ago, and while it still rings true, what I remember more than anything now is the care people took with each other.
I also remember making sandwiches for rescue workers at one of NYU's dining halls. My roommate and I worked at a table across from a little boy and his mother, assembling ham, tomato, and mayo on white bread. I remember us giggling at the gobs of mayo the kid slapped on his sandwiches. "Is he trying to give the rescue workers heart attacks?" we asked each other. I remember it was a relief to giggle, and it was a relief to see the unintentional humor of this little kid very clearly in a one-sided competition with us to make the most sandwiches.
I mostly remember the generosity, the unspoken assumption that it was okay to lean on a stranger, if you let them lean back on you. And it wasn't like that only on the 11th and the 12th. It was like that for months. It was terrible and wonderful.