Re: What can you bring to the table in 1200 AD?
Since glass was already being made at the time, I would bring plans explaining how to make multi-lens microscopes, which was the groundwork for a lot of scientific breakthroughs, the most important one for the survival of an empire would be the discovery of bacteria and 'germs'.
With the ability to study things at a cellular level through microscopes, there would be great advancement in the health sciences taking place.
And I agree with the above poster, food production is the most important. With an abundance of food, more specialization is available, more scientists, more merchants, etc.
*back to drinking coffee*