Probably photography. I'd love a nice DSLR rig with a good selection of lenses and a course in how to make the most of it.
I'd certainly put more time into drawing and painting, those have been hobbies of mine since before I got into modeling, they got me into my previous profession of graphic design until I decided that I liked them better as a hobby than a business.
Gardening also, very relaxing and therapeutic hobby that.
Would probably also spend more time at the swimming pool staying in shape.