I think it's awesome that your company is giving you an opportunity to have a sabbatical.
How about crafts, such as sewing, jewelry making, woodworking, etc.? It's even something you could do with your children if they're not too young. I recently took a day off from work to take a pen turning class and I really enjoyed it. Now I have to buy a lathe in order to make more pens...
If I got the opportunity to have a sabbatical, I'd probably do some combination of crafts, learn the trumpet - using my husband's trumpet that has been neglected since grade school, and exercise a lot more.