Every time I go to PAX I'm asked by those that reside in the US to bring over some UK confectionary due to the fact that we seem to better at making it than those in the US. I did this with much success for PAX East and am more than willing to do so again for PAX Prime 2010.
Examples of British confectionary can be found here
If you really want to push the boat out I can also get some Thornton's Chocolate. It is a bit pricey though.
Let me know on this thread what you'd like and I'll see what I can do.