I've used tarps quite a bit with car-camping and last week used one while bike touring in northern MN. We expected and had variable weather. Tarps can offer a lot of protection for very little weight. We have a 10x12 silnylon tarp that weighs in just shy of a pound. Add in setup lines & rigging lines and stakes and we're at about 2 lbs. If you take two additional setup poles that can add a half pound(for 50 inch aluminum tent-type poles) to 1.25 lbs for a pair of adjustable hiking sticks. We had hiking sticks last week.

We also had a 4.5 lb two-person tent. Lows at night got down to the low 30's..we were comfortable and had a great trip.