Here's an ultralight combo, poncho for cover, black contractor bag as ground cloth, and a bivy from EMK. Great summer night, except for maybe the bugs, need some deet too.
![](http://i174.photobucket.com/albums/w111/Be_Prepared/DSCN0082.jpg)
Of course, if you use those ultralight bivy's too often, they probably won't hold up. We also sometimes use a fleece bag for summer, I think it was about $15 at the Coleman outlet near us, and it's good for 45 or so with a good base layer on. Also a nice thing in the back of the car in winter.