Modern characters sent to mythic setting

[pachristian]

The primary issues aren't technological - they're social. Remember that the people living in this pseudo-iron age world have their own lifestyle and traditions, and most important those lifestyle and traditions work for them. Nobody is found of a bunch of people, of any age, suddenly showing up and telling them they're doing things wrong. For an extraordinary character in a fantasy world, check out Gordon R. Dickson's The Dragon and the George series. In this series, Jim Eckert is sent back to a magical medieval world. He's a medievalist and knows his history and mythology extremely well. He can work powerful magic. He has good friends and allies. And he's still often overwhelmed by the different values and mores of the world. For a more cynical look, check out Robert Plunkett's A California Dreamer in King Henry's Court. 

On the technological issue, everyone always wants to focus on gunpowder. That ain't squat. The real revolutions came from canning (which allowed food to be preserved for long periods of time), high-speed long distance communication (i.e. telegraph), and mass production (the art of making parts with such precision that they were interchangeable). Medieval and Ancient worlds had "factories" where they produced in volume, but Eli Whitney's genius was to make all the parts interchangeable, so that if you had a surplus of springs, you could use them on the next batch of locks, and so on. Oh yes, and the  moveable type printing press, which allowed inexpensive production of multiple copies of books - starting with the Bible, but including scientific treatises and popular fiction. This in turn lead to a revolution in reading and writing.

Looking at popular "modern person in a savage world" books, I notice that the characters all seem to be athletes and outdoorsmen and fighters, and often someone who "doesn't fit in the modern era". Where that's not the case, they invariably have a protective ring of powerful friends (i.e. NPC's) to cover for them until they make their extraordinary contribution to the fantasy world.