You will need to secure a physical space for the duration of the jam to comfortably seat participants and have reliable Internet access (either wired or wireless) for all participants. You will also want to consider providing:
1. Access to all space and computing resources around the clock over the weekend. You can still hold a jam if you do not have 24-hour access to the space, but you should communicate the opening/closing hours to your participants well before the date. There will be a participant sign-up starting in early September and you will receive a list of the people who sign up.
2. Local IT support in case of problems with computers or internet connectivity.
3. Coffee and beverages & easy access to food.
4. Access to common game development tools and/or ability to download and install software. You might want to download this software onto machines or thumb drives before jam date to ease the use of the networks at the beginning of the event. Also be aware of the resources many companies make available to jammers, listed http://globalgamejam.org/jammer-resources here from the Global Game Jam event.
5. (Optional) Auditorium space to do an initial gathering on Friday, and post-Jam presentation on Sunday of the Jam.
6. Security (safeguard against theft of belongings).