wreaths
There are several prayers said in the orthodox church. They say prayers over each phase of death and burial. The prayers are usually accompanied by a vigil. This practice is said to separate the soul from the body and help it on its journey.
The funeral is held at generally held at a church. The gift of wreaths, crosses, or other religious symbols are welcomed at any point during the mourning period. It is particularly important to give crosses and wreaths to the deceaseds family. Not sending anything or bringing the flowers to the grave site is very appropriate in this religion.
If you are planning a funeral for someone who is Eastern Orthodox you should speak with the church on exact needs of wreaths. They will be happy to speak with you and you do not want to do anything that will offend anyone especially at this trying time. It is important to observe all of the important practices when dealing with mourning relatives.
Organ donation on the other hand is all right. It goes under helping people out even in death. In order to be an organ donor an eastern European would need to fill out an organ donor card in the presence of at least one witness. It is believed that the practice of helping others out in this way is referenced in the bible.
In eastern European families cremation is a big no. They believe that they should be returned to the earth. Bodies are dealt with by being put into a wreaths coffin and then buried into the earth. This is normally accompanied by a grave side service and mourners throwing some dirt on the coffin once it is in the grave.