I'd probably alternate between travelling for a couple of decades, taking notes and pictures and then 'settling down' living for a couple of years in a small town, working as a teacher or something, before moving on to another place so that my not-aging won't be noticed.
On my spare time I'd use my notes and photos to write books, about 5 for each century, noting what has disappeared, what has risen in its place etc. Then I'd make a digital copy of each book and send it out on the web, while storing the originals in some deep underground vault safe from wars and natural disasters.
I'd be the observer, making sure that human history was recorded and stored for later generations, or later species. (This of course means that I'd have to try all the new cool things as well... I got quite the addiction to adrenaline)