How can I open a frozen padlock? Spraying WD-40 didn't help and I don't have access to deicer spray at the moment. I'm not sure what else to try.
If you are miles from anywhere and you don't have anything with you described above and your survival depends on what's on the other side of the door there is a fairly unsavory way to thaw the lock to allow you to operate it; urinate on it. It's not pleasant but it will raise the temperature of the padlock and thaw any ice in the mechanism.
To add to the other answer that may not be as accessible due to the length of a Hair Dryer cord, here is what I do:
Wrap the lock in your hands and breathe on it. Use your hands to insulate the heat in. This usually opens it, and I usually take it somewhere warm to thaw out and apply the WD-40.
Other methods are if the lock is pure metal is to put a fire(cigarette lighter, etc) directly to it. The below link says to use a mug of a hot beverage. But from experience the hot liquid will be steam and if the weather is cold enough, this will turn to ice when it the lock. But if hold it close enough and have some barriers around it to protect against wind then it should work.