Most professional press attending E3 avoid "swag". It's unprofessional (plus it's usually tacky anyways!). For many fansites and retail reps, though, E3 is as much about the race to collect free t-shirts as it is to play some new games. For some of those, it's then also a race to get the crap up on eBay to try and make a buck.
As eBay searches will already how you, scalpers are already trying to offload all kinds of promo gear they grabbed from the showroom floor, whether it be t-shirts, figures or cheap promo facemasks.
Game Sniped has a good rundown of some of the "highlights" currently up for bidding. I won't link to the auctions individually here, but let's just say that if you're paying $US200 for a Nintendo coin, you're getting ripped off.
E3 Material [Game Sniped]