I'm good at travelling light, I like having only carry-on baggage if I'm just going away for a few days (saves time on arrival), and I long ago developed a foolproof system. I have a jacket with extremely large pockets. Before I get to the check-in, I transfer books, toilet bag and anything else heavy to my huge pockets. My bag (with about one change of clothes) is then well under the required weight. They don't weigh me, but if they did, I weigh less than the average pax even with all this extra stuff. Once safely through I repack my bag, and on the aircraft I put it under the seat in front.
I've no doubt someone here will complain, but I'm not breaking any rules or endangering anyone, and it works.