If I can transport things back and forth, I would probably go and max out a credit card and buy all of the gold that I can to bring with me for trade.

Then I would go to the library of Alexandria and use my cell phone to get photocopies of as many books as I possibly can, and in the downtime I would go to any open Street markets and purchase any cool relics that I can find.

Then I could come back and share some of the Lost books of Alexandria with the world and also have period correct relics that have somehow magically not been exposed to a thousand years of environmental corrosion.

Then again, that would probably also mess up their radioisotope dating but I don’t know if it’s specific enough to only cover a thousand ish years.

Maybe if I have a little more time to prep I can find some place that I know hasn’t been Disturbed and like put them in an airtight safe and store them for me to go back and ReDiscover now.