The trick to remember is that you'll want to take off your clothing while you're sleeping; otherwise the sweat your body creates while sleeping will soak into the clothing, diminishing its' thermal capabilities. At the temperatures you guys are talking about, it might not be such a big deal; but if you're talking about the weather we see up north here, it's the difference between life and death.

I have a sleeping bag the reduces to the size of a loaf of bread, and it's good for temperatures down to -10 Celsius (that's about 14 Farenheit for you guys). I have 550 cord and a military "hooch" (essentially a windproof canvas sheet about 10'x6' with tapering triangular ends, available at most army surplus stores) that can be used to make a low profile shelter (closed or open), that you can still hang your clothing from a string at the foot of your sleeping bag. I have a small air mattress that is light and can strap to the outside of my daypack. Again, that'll add warmth to you, since you and the sleeping bag won't be in direct contact with frozen ground.

My little daypack has this and a couple spare bits of clothing (in case I get wet; again freezing temps and water/moisture on body are not a good combo), two days worth of rations, and a camel back with 3 litres of water. There are other little things in there as well; matches, some knives,an axe, a small cooking pot and pan, etc. etc...

You also have to pack for the climate you're travelling in, and for how long you're gonna be out there. 2-3 days isn't so long, but extend that to a week, and your pack is gonna get larger.