Avalanche training
I started realizing that I know nothing about snow science, and I cannot read terrain well. In the backcountry that can be dangerous. You should be able to identify hazards, make a judgement when conditions are changing, assess basic avalanche risk, or at least know how to properly read avalanche forecasts and reports.
That lead me to signing up for an AIARE course this year. I feel like it's kind of a requirement for being out there.
The nice part is that in addition to some theory we also got to get out, tour around Mount Washington and dig some snow pits. Granted, there wasn't too much snow for digging pits, but we worked our way around it.
It was one of those days where you make your body explore its limits, with temperatures dropping down to -20F (windchill) or so. Cold enough that fingers go numb when you have to take off your mittens for longer than 20 Seconds. Makes every gear change a tightly planned strategic event.
Good class though - great guides and great group of students to be out with!