I took the NOLS Wilderness first aid class and I now teach a class for a Wilderness group here in TX. My class focuses on decision-making more than hands-on skills. I have seen a lot of Boy Scout classes like "put an onion on a burn" or "make a litter out of tree branches and duct tape". That stuff is all well and good but most of the stuff my folks do is not true back country. I saw a definition somewhere that "wilderness" is defined as a 30 min or more delay from EMS resources, and we run several trips a year that meet that criteria (backpacks, canoe trips, etc).
I teach some hands on skills, but more of what I teach is recognizing the things you need help with early and how to stabilize your patient until help arrives. Example: You are likely not going to be able to hike a 250lb man with a broken ankle, 2 miles back to the trail head. You are going to be much better off, sending help and stabilizing the patient until you can get an ATV or helicopter in to rescue your patient.
Every situation is different. I think the biggest decision for true back country is how much are you going to pack in? Every liter bag weighs 2lbs, a lot of drugs break down in extreme heat. I think most of wilderness EMS comes down to pre-planning and good decision making.
TLDR: Take your city skills and marry them with some sound decision making and that is most of Wilderness medicine (not talking about technical rescue at all, that is a whole nother beast)