Tokyo Big Site - Tokyo Big Sight is an exhibition hall in Tokyo.
The second panel is a Scooby Doo reference. The movie had just recently come out.
Zoik5! = Zoiks!
The third panel is a Matrix reference.
SPNK-R - the rocket launcher in the Marathon games from Bungie
Kekko Kamen - a hentai heroine who fights wearing a mask and nothing else

Piro speaks:
Kekko Kamen is... another matter. :P as with everything, all poking in good fun. Con's wouldn't be the same without the Large Bearded American Men in Cute Girl Outfits, now would they? :P

Omiket - a pun on or possibly a typo of Comiket
Note the strip number, SGD:55 1/2, because the strip that launched into Largo's flashback was chapter 2's strip 55.