What are your best tried and true life hacks for the field?

This about sums up everything one needs for the field.

For light infantry guys sleeping outside in subzero weather without tents or heaters, such as Fort Drum, NY or Alaska. A quick way to warm up your extreme cold weather sleeping bag is two 9 volt batteries shorted to each other. Much caution is needed as they will get hot enough to burn you or melt your sleeping bag. I stored each one inside a wool sock inside my sleeping bag. Connect them for about one minute, disconnect then store in socks again. When you wake again freezing reconnect for another minute the store again. Used like this two batteries will last about three days at minus 20 degrees.

And powder for the feet and other areas that chafe

I used to pack a body bag to sleep in with my poncho liner, keeps you warm and dry when it's mildly cold outside, like always at Ft. Lewis.

SPC Nate Reynolds - So true. Even up in Alaska, you can sleep right on the snow and stay completely dry.

pack as much as one can carry comfortably..

That's a pretty good idea