In reply to Ash Routen:
LiFeS2 (the usual lithium AA primaries) cells perform well in the cold, but their useful capacity drops, especially with higher loads: (https://data.energizer.com/pdfs/lithiuml91l92_appman.pdf). Conversely, the cells do get warmer as they discharge. Better not loose that heat and insulate your battery holder. But the cells do have a built-in thermal shutdown switch (usually around 85C), while you are probably unlikely to trip that in normal use, it is a consideration if you have the box really well insulated and the cells under high load. Test it beforehand
If you need to do any soldering in your setup, select the proper solder - normal (mostly tin) solders are only good for normal temperatures, tin gets "brittle" in very cold conditions (as the Scott expedition allegedly discovered to their peril).
Anyways, you would need a DC to DC (5V USB?) converter. There are many types of those - pulse or continuous, boost type, etc. Unfortunately I am not able to provide a tip for the best one for your application - you might try asking around on some flashlight geeks forums like candlepowerforum or similar or your local electronics geek
Consider diversifying your power - if most of your devices need charging (not running on the AA cells directly), take a solar panel with some lightening of your battery haul. It's always better to not rely on just one power source and electronics box that could fail.
You could also consider other battery chemistries and industrial cells if your devices permit it - the LiFeS2 gives 1.5V, but there are other lithium primary cells (CR123A?) that work well in the cold and have higher voltage (which is usually better for the converter). Military uses LiSO2. But that's another can of worms - these are restricted for transport...