Each missionary should be encouraged to have some slides (digital projection), or a DVD of their ministry. One word of caution is that there needs to be a time limit. Most missionaries are sensitive to this, but some easily fall victim to telling a story about every slide they show and if they have thirty or forty slides, even 15 seconds comment on each one can get out of hand. There is nothing wrong with telling a story with a slide, just make sure comments are limited to just a few slides. By having a pre-recorded track with the slides, you know just how long it will take.
Typically each missionary will come with a physical display that can be setup along a wall and allow people to view artifacts from the mission field, a map, some neat photographs, etc. There should also be a stack of the missionaries prayer cards and a sheet so people can sign up to receive periodic news letters by email and or snail mail.
Since these displays are often set up in hallways or fellowship halls, it is helpful for the conference director to continually encourage people to visit the displays.