If we travel back in time — indulge us for a moment here — we'd be completely screwed. We can hardly envision the situation depicted in Mark Twain's "A Connecticut Yankee in King Arthur's Court". We wouldn't be able to use our current technological knowledge to survive in the past. What is our technological knowledge anyway? We know about computers... that's not gonna be much help. It's not like we can build one from scratch. Where would you even get silicon in the past, anyway... No, we'd be totally screwed.
Here's a thought: would we be able to dominate the people in the past physically? We're far from giants here (we're Jewish and all), but wouldn't our barely-five-and-a-half feet frame tower over the fledgling ancestors? Perhaps not.
What about mental strength? Our deep knowledge of mathematics, including a trek through four semesters of calculus would surely come in handy! Sadly, we forgot most of it, and we can imagine that dropping knowledge of integrals would get us burned at the stake. Perhaps we could limit it to trigonometry? They had angles in the past, right?
Which brings us to chess. We're not exactly good at it, but wouldn't we, theoretically, be really awesome when compared to the players of the past? Take Ruy Lopez de Segura, considered by many the first unofficial world champion. (Jewish? Perhaps a marrano, but he did become a bishop, so we would say no.) He is best known for the (duh) Ruy Lopez opening... the simplest opening in chess! We know that opening! We bet we could take him!
Alas, our chess career (if you can call it that) peaked in high school, so we're a bit rusty. Still, better start practicing now! You never know where (or when!) it will come in handy...