I'm so envious - it's a great feeling going for that first WI, having stuck to CD all week and therefore already knowing that you're on your way to a meeting where you'll be praised and admired for weight reasons for once!
I'm sure you'll have a great loss, but a tip is to try not to have a figure in your head that you're reaching for. Many people talk about their first week's loss on the forum, and some people achieve fantastic numbers, sometimes into double figures. But remember that we're all different, and a 3lb or 4lb loss can really be a great achievement for some.
Having said that, don't forget to come back and tell us!