This behemoth of a sleeping bag was a constant companion for me on backpackingtrips during more than 10 years. When I finally weighed it, it turned the scale at 3,2 kilos (7 lbs). Needless to say it is no longer with me..
Fairly regular internal frame packs like these (65-75 liters) often weigh more than 3 kilos empty.
A classic tunneltent like the one above can weigh between 2-4 kilos depending on size and materials.
Summing up the collective weights of the above "three big ones" we land somewhere between 7-10 kilos. Taking this down to 3 kilos will make a lot of difference when you hoist it onto your back. The surprise is that it can be done a lot easier than many people think. My experience is that it can be done without sacrificing either safety or comfort in camp, which is the most common objection you get from people who usually have not tried it themselves. The whole concept of 3 for 3 is addressed at length in the book.
Here is an article that covers 343 more thoroughly.