A lot of good answers already, but I'll add a few more:
I always dress in layers or bring a wrap - room temps can vary and there is nothing worse than being uncomfortable to distract you.
Our regional conference always has a huge snack table, so food and treats are never in short supply. But if your conference doesn't, you might want to bring some hard candies or lollipops you can share - then you'll have something to suck on during sessions, and you can offer some to your neighbors and strike up chats.
I second JudScottKev's recommendation to leave your shyness at the door - you can always ask anyone attending what they write (or if they are an illustrator, what mediums they use), if it's their first conference, where they live, how long they have been writing, etc...and those questions can be jumping off points for conversations.
I'll second business cards with your contact info can be great - but also have somewhere for you to either write down people's contact info you meet and want to stay in contact with, or a place to collect and keep their business cards.
Regional conferences are a great way to network with writers and get rejuvenated after sessions about craft and process. But they are most successful when you go in with the intent to meet people, network, and rejuvenate, as opposed to putting all focus on the critique with the editor. And you can be most prepared for your critique by maybe have a couple questions of your own you'd like to ask - ie, listen to the critique, but if after the editor has critiqued your page, if there is time/opportunity to ask some questions, they you might want to have them ready - like if there is something about the character or scene or your writing that you have concerns about or specifically want feedback on.
Have fun.
~suki