Lots of good suggestions in this thread!! My 2 ¢’s
A $40 tyvek ground sheet/tarp
http://www.materialconcepts.com/products/tyvek/ground-sheet/ and basic bivy like the ($89 REI Minimalist) gives lots and lots of set up ‘options’
I like to set up the tarp like AZTtripper mentioned if I think it is going to rain, otherwise just toss the bivy on top ½ the tyvek, spread out my gear as handy/needed, toss the bag on top of the bivy, then during the night adjust as needed, for cold-bag in bivy, for light rain-pull 1/2 the tyvek over top of upper bivy and all my gear. Also this combo is light, packable, rain proof up to a point, has room to spread out your stuff and move/roll around, keeps your gear off the ground & under cover-hence no morning condensation, keeps the tiny desert ‘sticky’ vegetation you might bed down on in the dark at bay etc etc
Also I agree with using clothing as part of your insulation, I pick and choose from the following, depending on the expected trip conditions: A thin (will fit under the helmet) baklava, a 6 oz sleeveless down vest, a long sleeve light-weight wool undershirt, unpadded tights, full length leg warmers, knee warmers, arm warmers, a lightweight set of water proof ‘overgloves’ (tough enough to use around camp and loose enough to fit over your bike gloves in the night/morning or anytime when raining)
Well, I could go on and on but will stop now……. hey its sort of fun geeking out on all the gear choices….enjoy