Permanent furlough? Did the company go out of business? I'm assuming that you have no hope for recall?
Well, the best option is of course to fly - any flying job. Aside from that, I would utilize this time to do something that you've always wanted to do. Maybe get a masters degree, learn to cook, get a type rating that you've always wanted (not because it will make you competitive, but because you've always wanted to do it) volunteer at a local youth facility.
Think of it this way, you will be sitting in front of an interview panel at some point down the line. What are you going to tell them when they ask "So what have you been doing for the last two years?" You want to show them that you are interesting (so they will want to know more about you), that you took advantage of your furlough time to accomplish something. Of course, you'll also want to show them that you've flown whenever possible and done everything you can to stay current.
I hope this helps!
Lori