An old classic that works on many animals, a skilled person with a laser
pointer is a ferret's best friend. Many of them, for whatever reason, just don't
seem to get a pointer like this; don't be surprised if they completely ignore
it. They're usually cheap enough, so it's not going to cost a lot to experiment.
If they are the type to fall for it, you can give them a quick and easy workout
by waving it across the floor. Watch them race after it. Be sure not to aim it
at their eyes.
All it really takes to entertain a ferret is to keep things fresh and to use
some ingenuity. All of these ideas are proven winners, but creating your own
isn't difficult either. Anything can occupy their attention if it's new to them.
Just be sure whatever you introduce provides no opportunity to harm them in any
way. That's the hardest part. You're the only person who knows what your animal
is capable of, so take the time to think things through, and you should never
have any problems.