Marmema, your confusion comes from the fact that at a Serbian "Slava" celebration, there are two things prepared to eat. The first is essentially koliva. This is prepared, I think, because at the Slava commemoration, one is praying for one's Christian ancestors who are departed.
The second thing prepared is the "kolach" -- which is a special bread. The priest cuts into the bread in the sign of the cross, and pours wine into this cross in the bread. The family members hold it and turn it around three times (as I recall) while singing the troparion of the saint.
Many Serbian parishes also serve a Slava celebration for their parish patronal feast.
Since we were received into the Orthodox Church via the Serbs, and since we were the first in our families to convert to Orthodoxy, we ourselves have a family "Slava", although we have rarely since been in a place where we have had a priest who knows how to serve the Slava service. The family Slava is second in veneration to each of us only to our personal patron saint.
We will give an icon of this saint to each of our children when they establish their own homes, and the tradition will, we pray, carry on down through the generations. Long after we personally have been forgotten, the Slava will be a reminder that once our family was not Orthodox, but that some crazy ancestor had the good sense to take the leap! :-) At the time of this feast, the original conversion of the family will be commemorated.
I think it is a wonderful tradition. During the harshest days of Ottoman rule, when all other religious observances were often snuffed out and priests unavailable, the Serbs never stopped having a Slava commemoration, led by the head of the family. It it not an exaggeration to say that in some places and times, only the Slava commemoration kept the faith alive within certain families.
Thank you Agrarian for a nice description. I make the zhito/kolyivo even if the priest is not around. Of course I do not make the sign of the Cross with wine over it but simply ask for blessing by prayer. And the bread, oh well, I never mastered that part -- tried once and it resembled a rock in size and consistency (oops!).
Agrarian also touched on another part of Slava which I neglected. Cities, organizations and so on in Serbia have a patron saint -- and therefore their own Slava. Many people in Serbia refer to significant dates by Church calendar name rathere than the Roman date -- such as "the Agreement on the day of Assumption" or "the St. Vitus' Constitution," etc.