I see a lot of guns come through courses in the US and overseas in Arctic conditions.
At my last DM Course, here are issues that some attendees experienced:
Frog Lube gummed up in cold weather like adhesive mixed with sand. I specifically recommend Slip2000 or some type of thick oil for the AR family, and have done so for years now. CLP will work, but doesn't have the staying power of Slip200 EWL. Motor oil works too, but be aware of detergent additives if that's something you're worried about.
Wolf might run for a few hundred rounds, but once a gun cools, the chamber can be caked with the laquer, and subsequent attempts to make it work will result in FTExtract malf's, even with brass case. This shut down a Noveske AR15 right in the beginning of the Culmination Exercise on Day 2 of the course.
Aluminum gas blocks have no place on an AR15 or AR10 carbine or MLGS. I've known this since 2002 after seeing what happens when you run a DPMS Lo-Pro on high volume. Short-stroke, gas leakage, coefficient of thermal expansion between steel and aluminum means don't do it.
If you are going to take your rifles and carbines into extreme conditions with lots of humidity and temperature shifts, I recommend Cerakote on all external surfaces where possible. The maintenance difference is night and day. Pay close attention to your torx and allen head fasteners, as they accumulate rust the fastest. Then comes the lock ring and receiver end plate, along with the muzzle device.
The flash hider I got from Precision Firearms is nitrided, and is becoming my favorite of all the units I've used over the years.
Set up your sling correctly before you attend training, or get some introductory AR15 training that includes sling set-up.
I can Parrot what Pat says about Mags, Extractor, Ammunition, Lubrication, which is a basic foundation for any mag-fed repeater.