All of Civilization’s Knowledge
There’s a great poster over at The Long Now Blog that claims to be all you’ll need to know should you find yourself transported to the far-distant past. Nuggets include: “Germs spread disease and can live anywhere” and “Heat milk to just below its boiling point: It wont curdle and 99.999% of the bugs in it will be killed. Congratulations! You just invented pasteurization.”
Kind of reminds me of a short story idea I came up with over coffee with Russell Davies: All the famous science fiction writers were actually time travelers with big plans to go back and get rich by inventing things before the person who was actually responsible. Problem is, when they get back they realize they don’t actually know how to make anything, so they’re stuck just writing about stuff instead.
Maybe I’ll get around to writing it one day.
Hi, I'm 
nice brother.
in mostly harmless – the fifth hithchikers’ guide to the galaxy book – Arthur Dent gets trapped on a planet which is similar to earth’s pre-history.
he realises that as a man from the future he can invent the future – but as you point out, he doesn’t actually know how to make anything.
he finally finds a role making sandwiches – the only technology he could create himself ;)
FX
I always thought I was the only one that worried about being absolutely useless if I was transported to the past. I even regretted not studying engineering for a minute once..once.