That’s Cabin Baggage or Hand Luggage for those of you in the English speaking world outside of the US.
A liter of water weights 1 kilogram. Collect and fill containers, put in a pillowcase or plastic bag, then lift water with one hand and your luggage with the other. Obviously you can divide your luggage and contents into several piles and weight them individually.
When the weight is too close to call or if airport purchases will add more than a few ounces I do the following.
Separate gear into three piles: 1) OK to discard if overweight, 2) Carry, wear or stuff, and 3) Everything else. Number 1 and #2 go in their own small bags and are packed on top for easy access. Since cabin luggage allowances dropped I’ve always packed this way but have never had to throw anything in the trash.
The #2 Throw Away pile on the last trip was a poncho, two bags of munchie mix (nuts & raisins, dried anchovies & peanuts, and M&Ms) that totaled half a pound, a paperback (but only because I had an eBook reader) and a 3-way extension plug that allowed charging 3 things at the same time.
The #3 Wear or Stuff was the heaviest things (most of which I can’t remember) that were small enough to fit in the cargo pants of my shorts, a pair of long pants, synthetic travel towel and it’s case, and the long underwear pants used at the Cameron Highlands. Had the luggage been overweight I intended to put on the long pants, tie the long underwear around my waist and stuff them and the travel towel case down the front of my pants.