I get obsessive about kit weight, because:
a) I actually use my kits frequently and
b) my wife is not as strong as me

8 Lbs is plenty light, the bag I carry in the truck at all times, and gets used on SAR and other situtations weighs in at a hefty 25 pounds, but that's because of the water on board (2 liters) as well as some tools that I need to carry in the kit for first-responder stuff (heavy cable cutters for car batteries, a pretty good sized first aid kit, a fleece blanket, and more stuff. The bag is designed for spending the night whereever I happen to be, ranging from the woods to the rehab tent at a large-scale incident. Unfortunately, in winter, it gets quite a bit heavier, as the sheer volume of stuff increases.