Since it was suggested on my last NSF proposal question, I thought I might also tap the collective brain on the question of broader impacts and synergistic activities. These concepts are still slightly unclear to me, though I understand them a lot better than I did when I wrote this blog post (which actually resulted in some pretty good advice). So let me ask:
What are some examples of synergistic activites and activities with "broader impacts" that many of us are doing, but haven't thought of to list in our NSF proposals? What are some ones we probably should be doing, but maybe aren't?
I'm particularly interested in the answers for young mathematicians. Most of the proposals I've read are from more senior people, who could point to their track record of mentoring graduate students and postdocs, or things like editing journals, in a way someone my age really can't.