Reddit reviews Field Guide to Wilderness Medicine: Expert Consult - Online and Print

For Wilderness: Auerbach or the WMI/NOLS Handbook. There are also CME wilderness options out there through WMA.

Before PA school I was a ski patroller and SAR team member for almost 10 years. Having done a bunch of first aid in the woods, both Auerbach's book and the NOLS book are great for skills. More important than hard skills are decision making. To that end I'd highly recommend taking a wilderness medicine class. Or Avy I/II if you're a skier. The hard part is deciding when to make the call to evacuate.