Business cards for new connections and pre-printed return-address-label-style stickers for vendor sign-ups and drawings, so you don't spend all your time writing your particulars.
A snuggly shawl for too-cold rooms, comfy layers and your favorite hold-all.
Your laptop, fully charged, with an extension cord for your adapter.
Google docs versions of your itinerary and conference schedule with sharing enabled.
Openness to speak to everyone you sit down beside. These are YOUR people. For introverts like myself, this can be the hardest, but ultimately most rewarding aspect of conferencing.
Committment to get the most out of the sessions, the backchannels, and the exhibits. This will require GTD or some sort of organizational scheme to separate out what you need to hang onto versus that which isn't right for you, right now.
The wherewithal to get up and leave the session if it's not meeting your needs without guilt.
I will be working on the last point in particular. Even at the national conference level, most professional development for school librarians is still undifferentiated. I have found that I get more from sessions on topics about which I know absolutely nothing rather than choosing those attractive-soundings sessions which touch upon areas in which I am already working. I get more from stretching myself into new areas of our profession rather than sitting in sessions which are replicating information I am gleaning from my PLN on a daily basis. So if you could lead a session on the topic, I would say sitting in it is probably not the best use of your precious professional development time....
see you in Charlotte!