You'll want to start by setting up a sound system so everyone can hear what speakers are saying. For small gatherings, that's not necessary but for larger ones it is.
Set up a microphone and speakers in the area you've set aside for the program. You can have other microphones, mobile microphones and several sound systems if you need them.
Get out cameras, camcorders, tape recorders or anything else you want to use for recording your family reunion. Put them in a convenient location so you don't have to hunt for them later.
Many family members will take photos with their own cell phones or digital cameras but the odds are you'll never see those photos. You'll want your own record to use later on if you choose to do a memory book.
Set up a separate area for laptops, scanners and copiers. Family members who are interested in genealogy will likely separate themselves out and you'll want them to have an area that is easy to use but doesn't disrupt what others are doing. Be sure to include a couple of power strips (extension cords) so those who brought their own laptops or other electronics have a place to plug them in. Add some easily movable chairs so they can sit down and form small groups.