Wear a conservative suit, including a tie.
Bring plenty of copies of your resume, no longer than 1 page. Carry them in a simple leather portfolio or small briefcase or professional bag, not a backpack.
Make sure your applications are published if you are ready to interview. I'd recommend having a prep company scrub your resume and app prior to the event/publishing but you're kind of behind the ball on this one. I recommend Spitfireelite.com for prep, I used them and received CJO's from UAL, DAL and SWA. Worth every penny in my opinion.
Practice a 3-5 minute introduction speech for yourself in case you get in front of a recruiter and they ask you to tell them a little about yourself, be able to pair it down as needed if they ask for a shorter version. Be prepared for if they ask you to tell them something about you that isn't on your resume. Think of what kind of answers you would give to a Tell Me About A Time (TMAAT) story that you might be asked, there are tons of examples on these forums. Plan your answers in the STAR format Situation, Task, Action, Result.
Bring mints, there will also be plenty on the different vendor tables.
Talk to as many companies as you can, it'll get you experience with the interview type questions, build relationships and learn about the other companies that are there. Be polite and courteous to everyone, it's a good technique in general for life and you never know who you might run into.
Bring small snacks and water for when you're in line for four hours to talk to a legacy.
Go to the social events and meet people.
That should get you started I think. Stop by the Spitfire Elite table at booth 409 to chat. Also checkout their new podcast,
https://www.spitfireelite.com/podcast/.
-Mike