What should I look for when choosing a sleeping bag? 

Sleeping bags are rated by temperature. (If the one you're looking at isn't, definitely don't take it.) For FOP, bags should be warm to at least 20 degrees and should have 4-6 inches of loft (thickness when laid on the ground). Please note that participants are asked not to bring down sleeping bags on FOP unless they have a waterproof or water-repellant finish.