A small ground cloth, closed cell foam pad, and a light down sleeping bag will allow you (or the rescue victim) to sleep comfortably all night, or to warm up if you get hypothermic, combined with your tarp.
Since I converted to ultralight backpacking equipment, I always carry these items on all solo day hikes. If I get caught out overnight, the day hike simply becomes a safe overnight. My base weight (before adding food, fuel, and water) weighs just over 6 pounds for trips lasting from 1-unlimited number of days. Since the advent of ultralight gear, many people use a similar inventory to hike the entire Appalachian Trail.
Here's my complete gear list with weights in oz:
35F down quilt 17.2
Silnylon tarp, plastic ground sheet, aluminum gutter nail stakes 18.4
1800 cu in rucksack 10.1
closed cell foam pad 4.7
Kitchen: aluminum grease pot with foil lid, supercat alcohol stove, plastic fuel bottle, lexan spoon 4.5
2 soda bottles for water 2.6
trash compactor bag as a pack liner 2.5
utility bag (map,iodine, first aid, TP, knife, compass, whistle, LED light, firestarters, soap, tooth brush and paste,, etc) 12.8
wind shirt 0.8 oz/sq yd fabric 2.0
wind pants 1.1 oz/sq yd fabric 2.2
Propore O2 rain jacket 5.5
fleece hat 1.2
polypro long john bottoms 5.3
wicking long sleeve top 100 wt 6.7
running socks, 2 pr, 2.8
bug head net for sleeping 0.7
TOTAL: 99.2 oz, 6.2 pounds
I've used this gear on numerous backpacking trips in the Adriondacks and White Mountains from late May to early Sept. In the "shoulder seasons" earlier and later than those dates, I bulk up to a warmer sleeping bag.
I don't like to be forced to rely on a fire for warmth. Most people underestimate the vast amount of wood you need to collect before dark if you are to keep a fire going all night, you get essentially no sleep, and you can't be more than a little bit injured or you will fail. I'm prepared to make a fire if needed, but my first line of defense is the tarp/sleeping bag/pad combo.