What do a chosson and kallah do in the yichud room?
Does the kitzur shulchan aruch, shulchan aruch or mishnah berurah gives us the details as to what the chosson and kallah do in the yichud room?
Answer to question 1:
Chabad have an article.
Once inside the room, the couple breaks their wedding day fast. It is also a time when the bride and groom customarily exchange gifts. Many grooms use this time to present the bride with a diamond ring.3 The bride also dons all the jewellery which she removed before the chupah.
Chabad custom is noted.
At Sephardic weddings, the newlywed couple customarily waits until after the wedding reception before entering theyichud room, and witnesses are not asked to observe the couple's entry into the room.
Why: Jewish marriage is comprised of two stages, kiddushin (betrothal) and nisu'in(marriage).4 There are certain halachic authorities who maintain that the final stage of nisu'in is not finalized until the groom takes his bride to a secluded area where they spend some personal time together. Jewish law forbids a man and woman who are not married to each other from being secluded together. Thus entering the yichud room together is an act which symbolized their newly married state.
Kabbalistic Meaning is given.
Q2. The article gives no sources.
What goes on in a yichud room is really supposed to be no one else's business. That's why is called a yichud room ...
But, since you want to know, I can speak from my wedding as well as that of my relatives and close friends:
First, in most cases, the chassan and kallah are hungry because they have fasted the whole day, and sometimes, the bit of wine combined with the stress of the wedding, the people, the photo shots, etc. just enhances the hunger. So, they eat. In actuality, this may be the only time that they CAN eat, b/c even though they get a small table at the reception and the caterer places food there, that's for show. They're busy dancing and getting pulled away for photos and videos. They probably won't eat really until after the wedding, assuming that there are left-overs to take home.
Then, the kallah usually needs to change some part of her clothes - the shaitel goes on (for those that follow this custom,) sometimes the girdle / hose is changed and the shoes are changed. I changed my shoes from the hard patented leather shoes to black sneakers so that I could dance.
Then, usually, the chosson gives the kallah a yichud room present - could be anything, as long as it's significant and memorable. (Related to comment below - even though the chosson gave an engagement & wedding ring, I gather that this minhag developed partly as a way of the chosson's demonstrating immediate "commitment" to his obligations in the kesuvah to support the kallah with clothes and jewelry, etc. Also, in a sense, the day of marriage is like a "Yom Tov" for the new couple, and on Yom Tov, it is minhag for the husband to buy jewelry for the wife. What I've heard from someone a while ago. It's a nice minhag and after all, the ketuvah places the majority of the obligations of the chatan towards the kallah, not the other way around. Children, in a sense, are the kallah's gift to the chattan, but that comes about 9 months later. Besides, the present may be an incentive to start "things" sooner than later. The chattan can wait a while for his "gift"!)
Finally, they discuss who's paying the wedding bill ... just kidding - but it does sometimes happen, when couples fund their own wedding.
By that time, someone knocks on the door and tells them that the photographer needs to take more pictures.
I answered Q 1 (You asked .. did you really want to know all this??? Are you still single?) As for Q2, I have to edit this in later, IY"H