Cebu Pacific used to weight the hand carry at the entrance to the plane. It was so funny to see those passenger's faces when the ground crew put a tag on the bags and sent them to cargo hold.Just make sure you know your airline's rules (and whether they are enforced). A number of low-cost carriers in Europe and Asia weigh carry-on bags. Heavy or oversize carry-ons are not allowed. And the "personal item" needs to be able to fit under the seat.
Pity 5J has stopped such a good practice.