I use a Western Mountain Bristlecone MF (ambient down to -10 degrees), a military issue poncho liner from US Calvary for hot nights. Also I have a Rivers West H2P Artillery Blanket that benjammin recommended for a little cooler nights but I use it mostly as a ground pad so if the temps start dropping it can be used as a blanket. Definitely a hard core blanket.
Western Mountaineering Poncho liner NSN: 8405-00-889-3683
River West
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Failure is not an option!
USMC Jungle Environmental Survival Training PI 1985