I think you should carefully consider going out without a sleeping bag. Some may have tried it and been fine, others may suffer. Folk sleep at different temperatures, and what is good for one person may not be good for another. I've just returned from Suffield in Canada where Medicine Hat had its first major floods in 10 years (lucky old me!!) and the prairie was awash for the first ten days. In this time, one of our new guys went down with hypothermia and was sent back to Germany.
He didn't take any cold weather gear, not even waterproofs. He was told on a briefing, as we all were, that MEDMAN 2 temperatures soar to 35-40 deg C. Most of our officers wore jungle boots in this muddy nightmare, and had omitted their goretex trousers, which more people are using these days. At night, the young lad crawled into his sleeping bag with wet kit on and then got soaked again the next day. By this stage, his body couldn't generate enough heat to combat the cold, and he went down. Imagine he didn't take his sleeping bag?
OK, this was down to his bad admin in the field and a lack of knowledge. Personaly, I used a softie 6 with a fleece liner I bought in Canada, and I had a softie 3 at my disposal aswell. Wet proofs were used almost daily, Helly Hansen field jacket came out on more than one occasion, and my shemagh got an airing on my bonce aswell! I didn't use my norgie shirt, but I had it all the same. As Gary also says, NBC suit was always an option. Armoured life is easier than dismounted infantry because you don't have to carry all your kit, therefore you take all you could possibly need, as the RAF know when I checked in 57kg worth of kit!!!
Anyone new to sleeping in the great outdoors should take a sleeping bag with them, even if they don't intend to use it, at least until they get a bit of experience under their belt. Always take it if you are going to Dartmoor!!!
Stay warm by carrying more!
Spamel