The purpose of a literary exposition is to provide some background and inform the reader about the plot, character, setting, and theme of the work at hand. The runners' expo situation proved dissect-able in the same way.
Setting: Marathoners, half-marathoners, and even some 5Kers and little ones doing the token kid jaunt, crowd through a series of tents packed with everything runners like. PT tool demos, the latest, lightest shoes, discount shorts, socks, and new innovations like a bib holder (for your race number, not the eating aid), Odwalla juice samples, free boxes of Minute rice. Yup, full-size boxes for free.
Character: Every runner present is driven, satisfied with themselves, and/or disgruntled to have to pick up somebody else's race packet before 5. The first-timers are euphoric and nervous, the veterans drawn and sometimes curt, the friends and family or those out of shape show signs of feeling a little out of place.
Plot: My fellow runners and I must accomplish this - look up bib number if not already known at one set of tables, pick up bib and safety pins at another set of tables, pick up T-shirt and goodie bag at yet another set of tables. (Note, all of these tables are categorized by numbers and names and sizes.) Repeat as many times as necessary for all the people you're picking up race stuff for. Then proceed to make your way to every stand that's giving something away, from stickers to ... Hey, are they offering whole boxes of Minute rice for free?
Theme: Runners are a different race. Especially before embarking on 26.2 miles in which the last 6.2 miles feel like you left all your muscles back at mile 13.