I've been thinking about this kind of thing for a while too. I imagine that a few people could multi task, but few people could do everything and do them well in my opinion. The way i see it, to maintain proficiency takes not a small bit of intrest. Call it a hobby if you want. By taking the time to get good at Agriculture (SHTF style agri, I imagine even modern farmers would be hard pressed when the SHTF and they had to produce food) you may not be able to spend the time with medical training (something like agri that eats up alot of time just to be proficient). Sure some folks with military training that are currently paramedics that live on a farm may respond and say they have it all covered, but my guess is that most folks won't.
My group of people includes one Nurse Anestesia provider, one general surgeon, 6 nurses and 2 surgical techs. We got medical covered in spades. Most of the guys are gun types, and my brother and I are into martial arts, so arms are covered too. We even have a lady that has a couple of horses. As for different agri, one of the wives is into gardening, and my family is trying to get into it to, but where we lack is food prep and communications. A few of us have been around canning, but none have done it ourselves, and no one is into comms. We are either going to have to expand our skill set, or find more friends.
Jim
Edited thanks to public school