Like I told you, I won't be there. But I can throw out some ideas:
Make sure the Astro and TP community is well-represented. Bug them via meta and chat to come by and drop in. I suggest you work out timings so that at least one mod each is here. And of course, it would be nice if we hade more than one Phy.SE mod, so that decisions can be made immediately. Roping in an SE member (maybe CHAOS) would be great, though not sure if it's possible.
Discuss If it's possible, do we want to expand the scope of this site to include astronomy? . Also how far we are willing to go in expanding the scope. (EDIT by DZ) The possibility of a name change should also be discussed, since it goes along with any possible changes in scope.
Discuss if there are any TP questions unsuitable for this site (doubt it)&
Discuss how to address the (I think) prevalent "we don't want our questions to be mixed with high school homework"/"Users who have gotten rep from easy questions(eg me) should not moderate our posts" attitude at TP. Also research-level.See also: Area51 discussion on TP&P.SE overlapArea51 discussion on TP&P.SE overlap, post on MSO discussion on merger, Research-level tag proposal
Maybe ask common community members to prepare a meta post on the differences(if any) that one must take note of between the two sites. Since most of the rep gets transferred, we don't want high rep users not knowing that we handle certian things differently here. Or just discuss the differences first and decide if this is necesssary.