Dust off your resume and take the military up on some of their offers in OPM. Even if you don't need to change jobs, there's no feeling like the one you get when you have a great job offer. Sometimes, it's just a morale booster.
Do some volunteer work. Many charities have endured a lot of cuts in 2010, and 2011 looks more grim. My husband and I delivered Thanksgiving dinner to meals on wheels clients last year, and we met a lot of lovely souls, and received a much deeper appreciation for what we had. I'll do this again during my furlough. There are also mentoring programs and teaching opportunities in local schools. You might want to get security clearance for that activity now, so that if the opportunity arises in a week or so, you make a positive impact.