Hi OneGirlOneBoy:
First, good on your husband for signing up for the registry and going through with the donation. I have chronic leukemia and could find myself needing to go to transplant at some point and I'm so grateful there are people like your husband out there.
Will this be a stem cell transplant or will they be transplanting actual BM? If it's the former, the process is super-easy--just a few blood draws. If he'll need to have bone marrow aspirated, I won't lie--it's unpleasant. But the procedure doesn't take long (20 mins, start to finish) and the painful part is only a very small fraction of the overall time. Some folks get it done with some conscious sedation. I was sore for 3 or 4 days afterward because there's some bruising but nothing that kept me from my usual activities.
In terms of what he can do to be super-healthy I'm not sure. The Leukemia and Lymphoma society has great discussion boards on its website; I bet if you posted there you'd get a ton of excellent advice.
Good luck to him!
DS1 (11!), DD (8), DS2 (2)