You can approach this problem in two ways:
1) Dealing with the situation at hand
2) Seeking long-term solution - if your social anxiety has a profound impact on your life it should be dealt with with the help of a professional therapist.
I assume 2) is out of the question or perhaps you are already working on it. So some techniques to help in first case:
1) Concentrate on maintaining a straight posture, with your hands relaxed on your sides (don't fiddle)
2) Concentrate on listening and maintaining relaxed eye contact, don't speak too much if it feel forced, but ask questions and smile and nod to acknowledge your counterparty
3) Be prepared for a few standard question (like "What have you been up to recently?", "Which events have you attended so far?", etc)
4) If you feel like you are getting stressed, excuse yourself with a smile and go to the restroom or fetch a glass of water
5) If stressed and cannot excuse yourself (because you are in the queue waiting for example), change subject to discuss your counterparty as much as possible taking the focus off of yourself.