Realistically?  I'd probably spend most of it lying in a hospice bed, too sick to do anything.  I don't think there's such thing as a disease that leaves you in perfect health for 30 days, then kills you the day after.

Or maybe when the doctor told me I had 30 days to live, he meant it as a threat.  In that case, I'd probably try to come up with some kind of plan to stop the doctor from murdering me...