This was my favorite kottke.org post from last year,
"I wanted to ask for survival tips in case I am unexpectedly transported to a random location in Europe (say for instance current France/Benelux/Germany) in the year 1000 AD (plus or minus 200 years). I assume that such transportation would leave me with what I am wearing, what I know, and nothing else. Any advice would help."
In reading the Kottke thread for about 30 mins (it rules), I just had this thought: What if Michaelangelo (or some other prolific inventors) weren't that special. What if they were simply average Joe's like you and me that were transported back in time. They used their basic knowledge of stuff around them to "invent" things.
Honestly, besides the natural teleological questions this prompts, if I were transported back to the middle ages there's not all that much I'm sure I could invent. For example, I have no idea how a computer is actually built, from the ground-up. Maybe I could have a few acute scientific observations ("try penicillin!"; "use tungsten for your light bulb!", "b-b-boil that milk!") and I could probably derive Calculus. But... that's about it. The vast majority of human knowledge is culturally transmitted; few humans have cumulative "clones" of the current "repository" of human knowledge stored in their memory.
Yes. Though knowing that certain directions are promising, would help. You know where to search.
For example, I could not build a steam engine, but I know enough to describe how one could build a basic atmospheric steam engine, and that to improve upon it, you'd need to separate the condensation of the steam from the rest of the engine.
But I guess I would have a lot of problems, convincing any sane medieval person to take my ideas seriously.
You don't need to invent much. Think of what you already know:
Wash your hands before eating; boil the water before drinking; put toilet facilities downstream of drinking water; cover open wounds and keep them clean.
In short, you already know about the biggest contribution to human health: Just Stay Clean. Everything else is icing on the cake.
"I wanted to ask for survival tips in case I am unexpectedly transported to a random location in Europe (say for instance current France/Benelux/Germany) in the year 1000 AD (plus or minus 200 years). I assume that such transportation would leave me with what I am wearing, what I know, and nothing else. Any advice would help."
http://kottke.org/08/06/survival-tips-for-the-middle-ages
Jason even opened it up for comments.