1. Rotate on-call and incident response. No single person should be chained to e-mail and incident response over the holidays; that's just asking for inattention to come back and bite you. At minimum, rotate responsibility among several people over the holiday season. Maybe even consider breaking the rotation into smaller slots than normal to allow people more time with family. That way, when they are on call, they'll be more apt to closely monitor events.
2. Check security events and logs regularly. Don't slack off here just because the office is empty. Watch network traffic to ensure abnormally large data transfers are not occurring. Attackers use times when people are away to transfer out their caches of stolen data. If they're smart, they will send small amounts at a time, but even this may be noticeable on days when no one is in the office.
3. Take this time to do maintenance. Patch your systems, reboot what needs rebooting, and tune your IDS. Use the downtime to up your security.
4. Protect against malware. Update your malware signatures and run full scans of all systems. Attackers love to slip malware into fake greeting cards or holiday Web sites. Chances are something is already in your network and an attacker is waiting to use it. While users are out is the best time to scan systems and remove malware.
5. Feeling like the Grinch? Test your incident response plan. The holiday season is the best time to test your IR plan and understand if your team is truly ready. Of course, your co-workers will not be pleased with you (see item #1), so be prepared.
Working during the holidays is no fun, but our opponents never stop, so we can't either. Ensure your protections and response plans are in place, be diligent and proactive, and hope for the best.
By the way, we're running through January 3 an extensive survey on risk management and would appreciate your input.