Don’t spend the entire event talking to just one or two people. You’re there to meet as many people as you can, so as a general rule, don’t spend more than about ten minutes with any one person.
Make an effort to read at least one newspaper a day. (Or at least, part of one.) Keeping abreast of what is happening nationally and locally will help you make conversation with the people you meet.
It also improves your credibility and your perceived intelligence.