Some ideas...
Live session (Hangout style) about Askubuntu, how it came to be and what does it mean to the Ubuntu community.
Shirts! Ubuntu/Askubuntu shirts!!
Video showing with awesome graphics the Askubuntu site, some of the most active users in the site (And also robots like Jorge) and promoting the site (And even the 13.04 version which most likely be on the same day as the release).
Information about the site. For example, did you know askubuntu has more questions, users and visits than Unix & Linux.This has to count for something when trying to get a hold of the popularity around Ubuntu. It is also the 4th in amount of visits, users and questions per day. 5th in amount of questions. Something similar to the one that was done to github where it showed all popular git projects, amount of clones, developers, etc..