If you paid attention in high school you could bring mathematics up to about the 17th century, if you really paid attention you could even grab some stuff from the 20th (wtf vectors why did you take so long to figure out?) and the 19th.
Plus there is just so much basic stuff you know. Used boiled and sealed water to clean a wound. Bleeding a person only makes them feel good for a bit and does nothing else. Steel in cement makes cement better. Or in the case of this picture zinc and copper and lemon.