At last, some logic.
I remember checking in with Thomas Cook (although the flight was JMC then) at Stansted for a flight to Dalaman. The kids were just about 12 months old. Most people can probably imagine what you need to take onboard with twin babies for a four hour flight - two made up bottles of milk each, change of clothes for both and all the rest. We had a changing bag with all those things in.
I was surprised to be told to put the changing bag on the scales which I did. It was 8kg. The girl said this was not permitted as the hand luggage weight limit was 5kg. No problem here - I told her I had no hand baggage at all so we were actually 2kg under. She said that it was still not permitted to have an 8kg bag. We had been into Boots or somewhere and quite literally opened the changing bag, took out the Boots carrier bag, transferred about half of it into the Boots bag (holding up the entire queue at check in) and presented both to the girl. She asked that we put them on the belt one at a time and we had one at 5kg and one at 3kg. She said 'fine' and printed off our boarding passes. We then put the Boots bag of things back in the changing bag, right in front of her, took the boarding cards and left, everyone now happy.