There will still be lots of PFS games with open spots at the convention. If you want to play in PFS, just head to the PFS HQ Table and the folks there should be able to help place you in a game. There are also lots of seminars with PLENTY of open seats. Basically registering for events helps guarantee a seat at an event and build a schedule of the things you plan on doing. Additionally, there will be demos of the new Adventure Card Game and Pathfinder Online going on pretty much constantly. We also have short 20 minute delves where you can go hop in a mini-scenario with a Paizo employee GMing. There are open gaming rooms with tables set aside for people who might want to organize a game on the fly. If there is something on the schedule that you really want to get into, check in with the GM and see if any seats have opened up, though ultimately it is up to the GM if they would like to replace missing players.