"...the riches of ages are stowed, Anything and everything a chap can unload..."
I went way too far for that reference...
Anyway, here's a rundown of stuff you can usually find at the vendor hall;
DVDs
Albums (CDs)
manga
plushies
weapons
toys
POCKY
doujinshi
art
t-shirts and other clothes
Oh, and lots of people. people who won't be eating out tonight after all.