I was unsure about what kind of gift to bring to my first traditional Japanese dinner but, I picked a nicely wrapped bottle of wine.
It was a good choice because we drank it later that night.
In America, there are different ways to host a dinner party but, most of the ones I have been to start out by, waiting for most of the guests to arrive before preparing the meal and everyone socializes and has drinks
while the food is cooking.
Usually, one main course is served with a few side dishes, then a dessert 
and for some, more drinks at the end. From what I saw, a Japanese dinner party happens like this; A small amount of guests arrive very close to the same time and the food 
has already been prepared and is waiting on the table for the guests to enjoy.
Shortly after everyone meets and says hi, the eating and drinking begins. I find that the Main difference between Japanese and American dinner parties is that, at Japanese dinner there are small amounts of many different dishes that everyone shares all through the night and people take their time to talk and drink while they eat.
Also, the hosts let their guests eat first before they start to eat, as a sign of hospitality. Often in America, one large meal is eaten in a short amount of time, without a lot of talking while they eat. Everyone eats from what is on their own plate because there is a smaller variety of food and all of the choices fit onto one plate. Most of the talking and drinking 
happens before or after the main meal is finished.