It's kind of hard to describe... but you can buy anything from airbrushes to paints, to figures, to mecha kits, to videos/dvds, etc. in the dealers room. It all depends on what you're looking for.
You can check out piccys from previous Wonderfests here: http://www.wonderfest.com/news2.htm (click on either "Starship Modeler - Review and pics galore!" or "CultTVman - Great contest photos!")