The cassette--the first in a regular series Geronimo! plan to release dubbed Buzz Yr Girlfriend--includes six tracks and will be available for free at the show. You won't be able to get it anywhere else, so be sure to head out and get your copy!
For more info on the project, check out Geronimo! member Ben Grigg discussing it on AV Club. You can also see the band's video "Design Yourself a Heart" below.