How do you deal with boredom at work?

My job has some crushing downtimes, but from what I hear I may not be alone. Apart from randomly surfing the web, and assuming another job is not an option at this time, what would you do? I’ve already asked my manager if there was extra work and that lead nowhere. It is both a blessing and a curse, I am paid well to do nothing, which in my youth would have been great, but I’m way past the point in my life where something more is needed. Eventually I will look for a new job, but not in the next year so I need something to do in the meantime….productive is good (assuming I can’t do much to improve my work situation), but even if it is something like sudoku that is fine.