QS---Years ago, your number 3 was a possibility. At one time in the aviation industry when pilots had to estimate their takeoff weight, pilots would allow for 150 pounds per seat sold for adults and 60 pounds for children. As we progressed through time and the population became more obese, we had to adjust this number twice. Checked baggage going into the baggage hold area is always weighed and so is the fuel. The weight of the plane has already been locked into the computer, the freight agents, baggage handlers, gate agents and fuel suppliers all give us their weights and we punch those numbers into the computer. The only other weight that we have to estimate is the baggage that is being put into the overhead bins, which we have standardized. The on-board computer or the FMS does all of the math and a lot of the numbers have already been inserted and remains a constant. Then, we take into consideration wind direction and speed and that gives us our takeoff speed and also tells us how much runway we will be using. Over my 34 years, I only had to unload baggage maybe 3 or 4 times. Those bags go onto the next flight going to the same city and if necessary will be delivered to the preferred address left with the baggage check agent at the departing airport. Because the airlines make a lot of money transporting freight or mail, they are very hesitant to unload those items. Rule of thumb is that baggage comes off first.
However, in today's aviation environment, it is very seldom and maybe even unlikely that anything is unloaded. With people now having to pay for their luggage to be checked and any piece of luggage over 50 pounds costing extra, I noticed that people were being more conservative with packing their luggage.