Congrats on the baby. :) First off, I would not hug and kiss her in front of them, if possible talk to her beforehand and ask her how she feels about it and tell her you won't be offended either way by her response. Let her know that you would love nothing more than to kiss and hug her all day, but that you want to do what's right and what her parents will expect, and that you will take your cues from her. You don't want her to think you are being standoffish, but you would rather not offend anyone.
Japan was once a matrilineal society and some of those ways still pass on to this day. Son in law's are expected to be very helpful in the family, and not necessarily to ask if they can be helpful, but to just do it. Whether it's taking out trash, setting a table, carrying bags, it may not be asked, but it may be expected. Ganbare (gun-ba-day) is a word of encouragement meaning "don't give up," "good luck," and "keep trying" all rolled into one. Ganbare is perhaps the most unique and defining Japanese attitude, it is a belief and a way of life. Feeling sad? Ganbare. Feeling tired? Ganbare. As a westerner or 'gaijin' you are not expected to understand everything the Japanese understand, but it would be good to pay attention and follow their lead. Most westerners are looked upon as a sort of novelty, and depending on the situation they will or won't be accepted.
In Japan, giving fruit is very traditional, a single cantaloupe tied with a bow in a wicker basket can sell for 100-200 dollars. The fruit must be a flawless and perfect selection. Putting together a small (or large) basket of various fruits for her parents would probably be well appreciated. Try adding fruits you might not normally see in a fruit basket (of you make it yourself) like lemon, lime, kiwi, pomegranate, you can even add some dried fruits, candied fruits, chocolates, etc.
For your girlfriend, a leather bound journal, with a beautiful pen, and some type of sweet, whether it's chocolate or candies fruits, or anything you know she might like. Perhaps some flowers, but something different like orchids, or lily's (unless you know what her favorite flower is) and it should be in white, to represent the purity of a mother to be. You can add one red for your love if you like.
I welcome your thoughts, let me know if you want to talk more.