I wear jeans and a t-shirt, and hiking boots for trail riding in Kansas. This would most likely be fine for you too, but it depends on the riding establishment. Some will require that you wear boots with a half-inch heel (they should have some provided if they require this), and some will require helmets (also provided I should think) If you are not wearing a helmet, take a hat of some sort to keep the sun out of your eyes (and the ticks off your head). Some people don't like to rid ein jeans, but as long as your jeans are not really loose around the thighs you should be okay. You could also wear jods (although you might get weird looks if you're riding western!), or chaps. If it is really hot, I sometimes ride in shorts and half-chaps. Whatever you're most comfortbale in should be fine. If you ride now, your normal riding clothes should be fine. Just don't wear any thin pants (like dress slacks), as they will rub sores on your legs. If you are still in doubt, just wait untill you get to the US, and call the riding place and ask them waht they reccomend.