In a tent it isn't such a big deal, but still worth thinking of....since you don't want to be breathing into your sleeping bag, but do want to keep your nose warm, bring a scarf or similar. I have a woven wool scarf (lighter by far than the knit ones) and I wrap it around neck and face when I sleep in the cold. It stops my nose from feeling froze and the wool keeps insulating even with the condensation from my breath.