Arthur C. Clark once said "Any sufficiently advanced technology is indistinguishable from magic". What technologies do we have today that would look like magic to people from the past?
I think lasers are pretty wack when you think about them through this lens. A small, wand-like object in your hand can make light appear from seemingly nowhere. If it's powerful enough it can set things on fire or blind people. Not to mention larger ones like laser cutters or the LLD, used to destroy missiles midflight. Thats sure to blow some feudal peasant minds
Well we'd all be burned as witches, so hopefully you are bringing people forward in time, not tossing them backwards. I'd expect my time traveler to be stunned by nearly everything:
Flush toilet
Electrical anything
Telephone, speakers, TV
I took a networking course in college and loved it but you still can't convince me that radio isn't magic. Even knowing the mechanics of it doesn't help - it's so freaking crazy. Fiber optic data transmission is such an awesome technology but even that doesn't confuse me like radio, or broadcast tv.