Many bride and grooms stay at the reception until everyone else has gone so it is not required that the guests wait until they have departed before they leave. When you leave try to find one of the parents of the couple, or who ever is hosting the party and thank them for their hospitality. Try and say goodbye to the couple if you can. It is customary for only those guests attending the wedding to send gifts. You may, however still send one if you can't be at the wedding.
Some people like to send a gift to make up for their absence.
This is by no means compulsory though. WebWombat Pty Ltd. All rights reserved.