If you are planning to participate in an event and there is an Expo available (usually on a Friday and/or Saturday race weekend) then I would highly suggest that you plan to attend. They can answer any questions you may have about the event along with supply much needed instructions you may need to know for the race. This is also the place where most events plan for you to pick up your race bib and runner's packet. Packets usually include maps, event info, promotional pamphlets, discounts on future events and other free goodies. And we runners, love free stuff, especially t-shirts.
Today, I attended the RunSF Expo and spent about an hour wandering around sampling different types of energy bars and drinks. I picked up my race bib, runner's dri-fit t-shirt and timing shoe tag. I also had the opportunity to meet a well known running legend, but I'm going to save that story for another day. I've been getting a lot of best wishes from fellow runners and friends... with the race 2 days away it always helps. Thanks guys (and gals).