Back in time to 100 BC, what knowledge would you impart to the people?
gills: I know we look different, but really, we're all about the same; this is electricity; this is called a lens; this is the scientific method; keep your animals further apart; prosperity through trade, not war and looting; drink hot tea and beer; mix tallow and ash.Oh, and of course:
    e^ix = cos x + i sin x