Bring your game discs, especially any required for the main games e.g. Far Cry.
Bring some OS and driver discs - you need them most when they're nowhere to be seen!
Run Steam in Offline Mode. Turn off Steam, pull out your network cable or disable your wireless, and run Steam again. Choose to run it in offline mode and make sure you can run Half Life 2 DM.
Make sure you've got your coconuts.
Scan your entire PC for viruses.
Get all patches for your games and especially the main games. For Farcry, bring the install disc and download patches 1.3 and 1.4. Not sure what patch level will be used at the LAN yet (1.4 adds nice HDR but created bugs in the AI)