Not going this time, but this is my experience with past PAXes: there seems to be less good free swag every year. At some point, official merchandise booths started becoming more popular than unique freebies. Some of these shops have show exclusives, like Pinny Arcade pins, and a few run deals (for example, sometimes Udon discounts their artbooks on the last day of the show). The official Penny Arcade store always has exclusives every year.
Flyers, posters, postcards, stickers, buttons, etc. make up the majority of the freebies. Codes are also popular; they're often for DLC or betas, but sometimes you can get them for whole games. There's still a few free t-shirts to be had, and many booths run contests for things like PC hardware and/or give away special items for preordering whatever game they're showing off. Nintendo usually has one or two decent pieces of swag available just for trying a game, but they tend to be the exception nowadays.
One of my favorite things to collect at PAX lately is autographs, thanks to special signing sessions and whatnot. Got Hironobu Sakaguchi's in 2014 and Noriyoshi Fujimoto's (Dragon Quest VII producer) last year. I need to bring one of my Halo soundtracks to PAX sometime so I can get Martin O'Donnell's, since he often appears on game music panels there.
Regardless of whatever swag you end up getting, hope you have fun at PAX!
